As part of an ongoing investigation into the organization and regulation of the flavonoid biosynthetic pathway, two Arabidopsis thaliana expressed sequence tag (EST) clones (153O10T7 and YAY780) with high homology to leucoanthocyanidin dioxygenase (LDOX) or flavonol synthase (FLS) were identified. EST YAY780 was sequenced and found to encode a protein 49 to 78% identical to all LDOX sequences in the database. EST 153O10T7 was used to isolate a genomic clone encoding a protein with 59 to 61% sequence identity to petunia (Petunia hybrida) and potato (Solanum tuberosum) FLS. DNA blot analysis was used to screen the Arabidopsis genome for sequences related to FLS and LDOX and to determine the positions of the two clones on the RI map. The expression patterns of FLS and LDOX in etiolated seedlings moved to white light and in two putative regulatory mutants (ttg and tt8) were determined by RNA blot analysis. These studies indicate that FLS is an "early" flavonoid gene in Arabidopsis seedlings, whereas LDOX is a "late" gene. Furthermore, FLS is the first flavonoid enzyme identified in Arabidopsis that may be encoded by a gene family.

The complete mitochondrial DNA (mtDNA) of the nematode Trichinella spiralis has been amplified in four overlapping fragments and 16,656 bp of its sequence has been determined. This sequence contains the 37 genes typical of metazoan mtDNAs, including a putative atp8, which is absent from all other nematode mtDNAs examined. The genes are transcribed from both mtDNA strands and have an arrangement relatable to those of coelomate metazoans, but not to those of secernentean nematodes. All protein genes appear to initiate with ATN codons, typical for metazoans. Neither TTG nor GTT start codons, inferred for several genes of other nematodes, were found. The 22 T. spiralis tRNA genes fall into three categories: (i) those with the potential to form conventional "cloverleaf" secondary structures, (ii) those with TPsiC arm + variable arm replacement loops, and (iii) those with DHU-arm replacement loops. Mt-tRNA(R) has a 5'-UCG-3' anticodon, as in most other metazoans, instead of the very unusual 5'-ACG-3' present in the secernentean nematodes. The sequence also contains a large repeat region that is polymorphic in size at the population and/or individual level.

The DNA element governing the inducible expression of drug-metabolizing P-450c gene by xenobiotic treatments was investigated by gene transfer methods. A variety of dissected fragments from -844 to -1140bp region which was essential for the inducibility of P-450c gene were placed on the heterologous SV40 promoter for testing the inducibility. Mapping studies in combination with gel retardation assay defined the presence of the two xenobiotic responsive elements (XRE, XRE1, -1007 - -1021bp; XRE2, -1088 - -1092bp) composed of about 15 nucleotides which expressed the enhancer activity in response to xenobiotic inducers. The two XREs share 10 nucleotides in common out of 15 as expressed in the sequence CG/CTG/CC/TTG/CTCACGCT/AA and are arranged in the inverse orientation. They are different from DREs (drug responsive element) proposed previously (Sogawa, K. et al. Proc. Natl. Acad. Sci. 83, 8044-8048 (1986] and expressed a strong enhancer activity in response to 3-methylcholanthrene. The XRE shows a significant homology with glucocorticoid regulatory elements and apparently needs normal functions of a putative xenobiotic receptor for the inducible enhancer activity.

Streptococcal C5a peptidase (SCP), a recently discovered virulence factor of Streptococcus pyogenes, specifically cleaves the human serum chemotaxin C5a near its carboxyl terminus, destroying its ability to serve as a chemoattractant. We previously localized the SCP gene, scpA, to the 5.8-kb insert of the recombinant plasmid pTT1. Here we present the complete nucleotide sequence of scpA and its flanking regions. The gene initiates at a TTG codon and consists of 3501 base pairs, specifying a precursor protein of 128,252 daltons. Sequences resembling the promoter and ribosome-binding site of Gram-positive organisms are found upstream of scpA. The predicted amino acid sequence reveals the presence of a 31-residue signal peptide, putative cell wall spanning and membrane anchor domains. Regions of SCP show significant similarity to the sequences involved in the formation of the active site of the prokaryotic serine protease subtilisin. Results of Southern hybridization studies indicate that sequences highly similar to that of scpA are present in all serotypes of S. pyogenes tested.

More than 200 fusca mutants of Arabidopsis have been isolated and characterised, defining 14 complementation groups. Mutations in at least nine FUSCA genes cause light-dependent phenotypic changes in the absence of light: high levels of anthocyanin accumulation in both the embryo and the seedling, inhibition of hypocotyl elongation, apical hook opening, and unfolding of cotyledons. In double mutants, the fusca phenotype is epistatic to the hy phytochrome-deficiency phenotype, indicating that the FUSCA genes act downstream of phytochrome. By contrast, the accumulation of anthocyanin is suppressed by mutations in TT and TTG genes, which affect the biosynthesis of anthocyanin, placing the FUSCA genes upstream of those genes. Regardless of the presence or absence of anthocyanin, fusca mutations limit cell expansion and cause seedling lethality. In somatic sectors, mutant fus1 cells are viable, expressing tissue-specific phenotypes: reduced cell expansion and accumulation of anthocyanin in subepidermal tissue, formation of ectopic trichomes but no reduced cell expansion in epidermal tissue. Our results suggest a model of FUSCA gene action in light-induced signal transduction.

The sequence 5'TTGGPyCAAT 3' (the 'CCAAT box') is a constituent of the promoter region of many eukaryotic and prokaryotic genes and is believed to play a part in promoter function. A characteristic of the two fetal human globin genes (A gamma and G gamma) is a duplication of a 12-base pair (bp) sequence containing the CCAAT box. Here we report a G----A substitution in the TTG sequence of the distal CCAAT box of the A gamma-globin gene in an individual with the A gamma (Greek) type of hereditary persistence of fetal haemoglobin (HPFH). This represents the first report of a natural mutation of the CCAAT box in a eukaryotic gene. The fact that this transition is associated with inappropriate expression of the A gamma gene in adult life suggests that the CCAAT box (or its surrounding sequences) may have a role in the developmental control of gamma-globin genes.

The gene for protein A from Staphylococcus aureus was cloned into pBR322 in Escherichia coli. An immunoassay was used to detect production of the protein. Protein A produced in E. coli was found in the periplasmic space and was purified and concentrated by IgG-Sepharose affinity chromatography. DNA sequence assay of the gene revealed a region with the general features of a prokaryotic signal peptide and a fifth structural region homologous to the four repetitive regions found earlier by amino acid sequence determination of the mature protein. Upstream from the structural gene there is a possible promoter region and a ribosomal binding sequence typical of gram-positive bacteria. The initiation codon is TTG.

In the enteric bacterium, Escherichia coli, acyl coenzyme A synthetase (fatty acid:CoA ligase (AMP-forming) EC 6.2.1.3) activates exogenous long-chain fatty acids concomitant with their transport across the inner membrane into metabolically active CoA thioesters. These compounds serve as substrates for acyl-CoA dehydrogenase in the first step in the process of beta-oxidation. The acyl-CoA synthetase structural gene, fadD, has been identified on clone 6D1 of the Kohara E. coli gene library and by a process of subcloning and complementation analyses shown to be contained on a 2.2-kilobase NcoI-ClaI fragment of genomic DNA. The polypeptide encoded within this DNA fragment was identified following T7 RNA polymerase-dependent induction and estimated to be M(r) = 62,000 using SDS-polyacrylamide gel electrophoresis. The N-terminal amino acid sequence of acyl-CoA synthetase was determined by automated sequencing to be Met-Lys-Lys-Val-Trp-Leu-Asn-Arg-Tyr-Pro. Sequence analysis of the 2.2-kilobase NcoI-ClaI fragment revealed a single open reading frame encoding these amino acids as the first 10 residues of a protein with a molecular weight of 62,028. The initiation codon for methionine was TTG. Primer extension of total in vivo mRNA from two fadD-specific oligonucleotides defined the transcriptional start at an adenine residue 60 base pairs upstream from the predicted translational start site. Two FadR operator sites of the fadD gene were identified at positions -13 to -29 (OD1) and positions -99 to -115 (OD2) by DNase I footprinting. Comparisons of the predicted amino acid sequence of the E. coli acyl-CoA synthetase to the deduced amino acid sequences of the rat and yeast acyl-CoA synthetases and the firefly luciferase demonstrated that these enzymes shared a significant degree of similarity. Based on the similar reaction mechanisms of these four enzymes, this similarity may define a region required for the same function.

We have determined a 180 kb contiguous sequence in the replication origin region of the Bacillus subtilis chromosome. Open reading frames (ORF) in this region were unambiguously identified from the determined sequence, using criteria characteristic for the B. subtilis gene structure, i.e., starting with an ATG, GTG or TTG codon preceded by sequences complementary to the 3' end of the 16S rRNA. Four rRNA gene sets, 7 individual tRNA genes and 1 scRNA gene were identified, occupying 20 kb in total. In the remaining 160 kb region, 158 ORFs were identified, suggesting that 1 ORF is coded on average by 1 kb of DNA of the B. subtilis genome. Among the 158 ORFs, the functions of 48 ORFs were assigned and those of 11 ORFs are suggested through significant similarities to known proteins present in data banks. However, the functions of more than half of the ORFs (63%) remain to be determined.

Tumors with somatic mutations in the proofreading exonuclease domain of DNA polymerase epsilon (POLE-exo*) exhibit a novel mutator phenotype, with markedly elevated TCT→TAT and TCG→TTG mutations and overall mutation frequencies often exceeding 100 mutations/Mb. Here, we identify POLE-exo* tumors in numerous cancers and classify them into two groups, A and B, according to their mutational properties. Group A mutants are found only in POLE, whereas Group B mutants are found in POLE and POLD1 and appear to be nonfunctional. In Group A, cell-free polymerase assays confirm that mutations in the exonuclease domain result in high mutation frequencies with a preference for C→A mutation. We describe the patterns of amino acid substitutions caused by POLE-exo* and compare them to other tumor types. The nucleotide preference of POLE-exo* leads to increased frequencies of recurrent nonsense mutations in key tumor suppressors such as TP53, ATM, and PIK3R1. We further demonstrate that strand-specific mutation patterns arise from some of these POLE-exo* mutants during genome duplication. This is the first direct proof of leading strand-specific replication by human POLE, which has only been demonstrated in yeast so far. Taken together, the extremely high mutation frequency and strand specificity of mutations provide a unique identifier of eukaryotic origins of replication.

A genomic clone encoding flavanone 3-hydroxylase (F3H) was isolated from Arabidopsis thaliana. The deduced amino acid sequence is 72 to 94% identical to all previously reported F3H proteins. Low-stringency DNA blot analysis indicated that F3H is encoded by a single gene in Arabidopsis. The F3H locus was mapped to the bottom of chromosome 3 and therefore does not correspond to any of the 13 flavonoid-deficient transparent testa mutants for which a map position is known. Analysis of gene expression in etiolated seedlings exposed to white light and in two putative regulatory mutants, ttg and tt8, demonstrated that the Arabidopsis F3H gene is coordinately expressed with chalcone synthase and chalcone isomerases is seedlings, whereas dihydroflavonol reductase expression is controlled by distinct regulatory mechanisms. The F3H gene may represent a pivotal point in the regulation of flavonoid biosynthesis because its expression is coordinated with different subsets of genes in different plant species.

Arabidopsis trichomes are branched, single-celled epidermal hairs. These specialized cells provide a convenient model for investigating the specification of cell fate in plants. Two key genes regulating the initiation of trichome development are GLABROUS1 (GL1) and TRANSPARENT TESTA GLABRA (TTG). GL1 is a member of the myb gene family. The maize R gene, which can functionally complement the Arabidopsis ttg mutation, encodes a basic helix-loop-helix protein. We used constitutively expressed copies of the GL1 and R genes to test hypotheses about the roles of GL1 and TTG in trichome development. The results support the hypothesis that TTG and GL1 cooperate at the same point in the trichome developmental pathway. Furthermore, the constitutive expression of both GL1 and R in the same plant caused trichomes to develop on all shoot epidermal surfaces. Results were also obtained indicating that TTG plays an additional role in inhibiting neighboring cells from becoming trichomes.

OBJECTIVE

Strict lifelong compliance to a gluten-free diet (GFD) minimizes the long-term risk of mortality, especially from lymphoma, in adult celiac disease (CD). Although serum IgA antitransglutaminase (IgA-tTG-ab), like antiendomysium (IgA-EMA) antibodies, are sensitive and specific screening tests for untreated CD, their reliability as predictors of strict compliance to and dietary transgressions from a GFD is not precisely known. We aimed to address this question in consecutively treated adult celiacs.

METHODS

In a cross-sectional study, 95 non-IgA deficient adult (median age: 41 yr) celiacs on a GFD for at least 1 yr (median: 6 yr) were subjected to 1) a dietician-administered inquiry to pinpoint and quantify the number and levels of transgressions (classified as moderate or large, using as a cutoff value the median gluten amount ingested in the overall noncompliant patients of the series) over the previous 2 months, 2) a search for IgA-tTG-ab and -EMA, and 3) perendoscopic duodenal biopsies. The ability of both antibodies to discriminate celiacs with and without detected transgressions was described using receiver operating characteristic curves and quantified as to sensitivity and specificity, according to the level of transgressions.

RESULTS

Forty (42%) patients strictly adhered to a GFD, 55 (58%) had committed transgressions, classified as moderate (< or = 18 g of gluten/2 months; median number 6) in 27 and large (>18 g; median number 69) in 28. IgA-tTG-ab and -EMA specificity (proportion of correct recognition of strictly compliant celiacs) was 0.97 and 0.98, respectively, and sensitivity (proportion of correct recognition of overall, moderate, and large levels of transgressions) was 0.52, 0.31, and 0.77, and 0.62, 0.37, and 0.86, respectively. IgA-tTG-ab and -EMA titers were correlated (p < 0.001) to transgression levels (r = 0.560 and R = 0.631, respectively) and one to another (p < 0.001) in the whole patient population (r = 0.834, N = 84) as in the noncompliant (r = 0.915, N = 48) group. Specificity and sensitivity of IgA-tTG-ab and IgA-EMA for recognition of total villous atrophy in patients under a GFD were 0.90 and 0.91, and 0.60 and 0.73, respectively.

CONCLUSIONS

In adult CD patients on a GFD, IgA-tTG-ab are poor predictors of dietary transgressions. Their negativity is a falsely secure marker of strict diet compliance.

Coleoptera is the most diverse group of insects with over 360,000 described species divided into four suborders: Adephaga, Archostemata, Myxophaga, and Polyphaga. In this study, we present six new complete mitochondrial genome (mtgenome) descriptions, including a representative of each suborder, and analyze the evolution of mtgenomes from a comparative framework using all available coleopteran mtgenomes. We propose a modification of atypical cox1 start codons based on sequence alignment to better reflect the conservation observed across species as well as findings of TTG start codons in other genes. We also analyze tRNA-Ser(AGN) anticodons, usually GCU in arthropods, and report a conserved UCU anticodon as a possible synapomorphy across Polyphaga. We further analyze the secondary structure of tRNA-Ser(AGN) and present a consensus structure and an updated covariance model that allows tRNAscan-SE (via the COVE software package) to locate and fold these atypical tRNAs with much greater consistency. We also report secondary structure predictions for both rRNA genes based on conserved stems. All six species of beetle have the same gene order as the ancestral insect. We report noncoding DNA regions, including a small gap region of about 20 bp between tRNA-Ser(UCN) and nad1 that is present in all six genomes, and present results of a base composition analysis.

Remodeling of small arteries is essential in the long-term regulation of blood pressure and blood flow to specific organs or tissues. A large part of the change in vessel diameter may occur through non-growth-related reorganization of vessel wall components. The hypothesis was tested that tissue-type transglutaminase (tTG), a cross-linking enzyme, contributes to the inward remodeling of small arteries. The in vivo inward remodeling of rat mesenteric arteries, induced by low blood flow, was attenuated by inhibition of tTG. Rat skeletal muscle arteries expressed tTG, as identified by Western blot and immunostaining. In vitro, activation of these arteries with endothelin-1 resulted in inward remodeling, which was blocked by tTG inhibitors. Small arteries obtained from rats and pigs both showed inward remodeling after exposure to exogenous transglutaminase, which was inhibited by addition of a nitric oxide donor. Enhanced expression of tTG, induced by retinoic acid, increased inward remodeling of porcine coronary arteries kept in organ culture for 3 days. The activity of tTG was dependent on pressure. Inhibition of tTG reversed remodeling, causing a substantial increase in vessel diameter. In a collagen gel contraction assay, tTG determined the compaction of collagen by smooth muscle cells. Collectively, these data show that small artery remodeling associated with chronic vasoconstriction depends on tissue-type transglutaminase. This mechanism may reveal a novel therapeutic target for pathologies associated with inward remodeling of the resistance arteries.

Type 1 diabetes and celiac disease are both immunologic disorders where specific HLA alleles are associated with disease risk. We have developed a radioassay for autoantibodies to tissue transglutaminase (tTG) following the report that this enzyme is 'the' endomysial autoantigen (EMA) of celiac disease. The radioassay for transglutaminase autoantibodies is similar to that utilized for detecting anti-islet autoantibodies. The 'cut-off' for the IgA autoantibody assay was established as 3 x 100th percentile of 184 healthy control subjects at an index of 0.05. Ninety-eight of 847 patients with type 1 diabetes (11.6%) had tissue transglutaminase autoantibodies (tTG). All EMA-positive patients were positive (49/49) for transglutaminase autoantibodies, as were 49/540 EMA-negative patients. Twenty transglutaminase-positive patients consented to intestinal biopsy and 15 biopsies were positive for celiac disease. All patients with a transglutaminase level greater than 0.70 (13/13) had a positive biopsy, while none (0/3) with a level <0.3 had a positive biopsy. The prevalence of transglutaminase autoantibodies was higher in diabetic patients with HLA DQ2 or DQ8. One third of DQ2 homozygous patients (22/68) expressed transglutaminase autoantibodies vs. less than 2% of patients lacking DQ2 or DQ8. A simple radioassay for IgA transglutaminase autoantibodies detects all endomysial antibody positive patients and detects transglutaminase autoantibodies in 5% of endomysial autoantibody negative patients. The prevalence of transglutaminase autoantibodies is associated with DQ2 and DQ8 and in particular DQ2 homozygosity. Autoimmunity to transglutaminase is remarkably prevalent amongst patients with type 1 diabetes expressing certain class II HLA alleles.

Upon prolonged treatment with various antiretroviral nucleoside analogs such as 3'-azido-3'-deoxythymidine, 2',3'-dideoxyinosine, 2',3'-dideoxycytidine, (-)- beta-L-2', 3'dideoxy-3'thiacytidine and 2',3'-didehydro-3'-deoxythymidine, selection of human immunodeficiency virus type 1 (HIV-1) strains with mutations in the reverse transcriptase (RT) gene has been reported. We designed a reverse hybridization line probe assay (LiPA) for the rapid and simultaneous characterization of the following variations in the RT gene: M41 or L41; T69, N69, A69, or D69; K70 or R70; L74 or V74; V75 or T75; M184, I184, or V184; T215, Y215, or F215; and K219, Q219, or E219. Nucleotide polymorphisms for codon L41 (TTG or CTG), T69 (ACT or ACA), V75 (GTA or GTG), T215 (ACC or ACT), and Y215 (TAC or TAT) could be detected. In addition to the codons mentioned above, several third-letter polymorphisms in the direct vicinity of the target codons (E40, E42, K43, K73, D76, Q182, Y183, D185, G213, F214, and L214) were found, and specific probes were selected. In total, 48 probes were designed and applied to the LiPA test strips and optimized with a well-characterized and representative reference panel. Plasma samples from 358 HIV-infected patients were analyzed with all 48 probes. The amino acid profiles could be deduced by LiPA hybridization in an average of 92.7% of the samples for each individual codon. When combined with changes in viral load and CD4+ T-cell count, this LiPA approach proved to be useful in studying genetic resistance in follow-up samples from antiretroviral agent-treated HIV-1-infected individuals.

We have found that tissue-type transglutaminase (tTG), also called TGc, TGase2 and Galpha(h), has the activity of protein disulphide isomerase (PDI). We have shown that tTG converts completely reduced/denatured inactive RNase A molecule to the native active enzyme. The PDI activity of tTG was strongly inhibited by bacitracin, which is a frequently used inhibitor of conventional PDI activity. It was substantially inhibited by the simultaneous presence of other potential substrate proteins such as completely reduced BSA, but not by native BSA. This activity was especially high in the presence of GSSG, but not GSH. The addition of GSH to the reaction mixture in the presence of GSSG at a fixed concentration up to at least 200-fold excess did not very substantially inhibit the PDI activity. It is possible that tTG can exert PDI activity in a fairly reducing environment like cytosol, where most of tTG is found. It is quite obvious from the following observations that PDI activity of tTG is catalysed by a domain different from that used for the transglutaminase reaction. Although the alkylation of Cys residues in tTG completely abolished the transglutaminase activity, as was expected, it did not affect the PDI activity at all. This PDI activity did not require the presence of Ca(2+). It was not inhibited by nucleotides including GTP at all, unlike the other activity of tTG.

Posttranslational modification (PTM) of islet autoantigens can cause lack of central tolerance in type 1 diabetes (T1D). Tissue transglutaminase (tTG), involved in PTM of gluten antigens in celiac disease, creates negatively charged peptides favored by T1D-predisposing HLA-DQ molecules, offering an attractive candidate modifying islet autoantigens in T1D. The highly predisposing HLA-DQ8cis/trans molecules share preferences for negatively charged peptides, as well as distinct peptide-binding characteristics that distinguish their peptide-binding repertoire. We screened islet autoantigens with the tTG substrate motif for candidate-modified epitopes binding to HLA-DQ8cis/trans and identified 31 candidate islet epitopes. Deamidation was confirmed for 28 peptides (90%). Two of these epitopes preferentially bound to HLA-DQ8cis and six to HLA-DQ8trans upon deamidation, whereas all other peptides bound equally to HLA-DQ8cis/trans. HLA-DQ8cis-restricted T cells from a new-onset T1D patient could only be generated against a deamidated proinsulin peptide, but cross-reacted with native proinsulin peptide upon restimulation. The rate of T-cell autoreactivity in recent-onset T1D patients extended from 42% to native insulin to 68% adding responses to modified proinsulin, versus 20% and 37% respectively, in healthy donors. Most patients responded by interferon-γ, whereas most healthy donors produced interleukin-10 only. Thus, T-cell autoreactivity exists to modified islet epitopes that differs in quality and quantity between patients and healthy donors.

Trichome development is dependent on gibberellin (GA) signaling in Arabidopsis thaliana. Using the GA-deficient mutant ga1-3, the GA-response mutant spy-5, and uniconazol (a GA-biosynthesis inhibitor), we show that the GA level response correlates positively with both trichome number and trichome branch number. Two genes, GL1 and TTG, are required for trichome initiation. In ga1-3, coexpression of GL1 and R, the maize TTG functional homolog, under control of the constitutive 35S promoter, restored trichome development, whereas overexpression of neither GL1 nor R alone was sufficient to significantly suppress the glabrous phenotype. We next focused on GL1 regulation by GAs. In the double mutant the gl1-1 glabrous phenotype is epistatic to the spy-5 phenotype, suggesting that GL1 acts downstream of the GA signal transduction pathway. The activity of a beta-glucuronidase reporter gene driven by the GL1 promoter was decreased in the wild type grown on uniconazol and showed a clear GA-dependent activation in ga1-3. Finally, quantification of GL1 transcript levels by reverse transcriptase-polymerase chain reaction demonstrated that relative to wild type, ga1-3 plants contained less transcript. These data support the hypothesis that GAs induce trichome development through up-regulation of GL1 and possibly TTG genes.

Amino acid variation at reverse transcriptase (RT) codon 210 (generally Leu-210 to Trp [L210W], TTG->>TGG) is occasionally detected after the initiation of azidothymidine (AZT) therapy. The impact of this variation on AZT resistance and viral replication was addressed by four different approaches. The frequency and genetic background of the L210W mutation in vivo were assessed by analyzing sera of AZT-naive and AZT-experienced patients by RT-PCR and DNA sequencing. The degree of AZT resistance (50% infective concentration [IC50]) of recombinant viruses constructed by using the RT of 21 clinical isolates was stratified by the presence or absence of the 210 mutation. The AZT IC50S of a panel of mutant viruses (with or without W-210) constructed by site-directed mutagenesis in an HXB2 background were assayed by using a HeLa CD4 plaque reduction assay. Finally, the effect of the 210 mutation on viral replication was assessed by replication competition of an AZT-resistant virus, RTMN (L-41/Y-215), and RTMN with the W-210 mutation in the presence and in the absence of AZT. In AZT-naive patients, tryptophan at RT residue 210 was rare. After AZT exposure, W-210 appeared in a minority of those patients, most commonly in association with L-41 and Y-215. The presence of W-210 increased the AZTIC50 by two- to fourfold, as determined by both the recombinant virus assay and site-directed mutagenesis. A significant replication advantage in favor of the wild-type L-210 over W-210 was observed, although the selection against the 210 mutant was two- to threefold lower when the viruses were grown in the presence of 5 microM AZT. In summary, the L210W mutation appears to be of marginal significance, conferring approximately two- to fourfold-reduced sensitivity to AZT compared with similar AZT-resistant genomes with L-210. The selection pressure against W-210 may account for the modest proportion of patients in which W-210 appears in vivo.

The gene encoding the IgG-binding protein G from Streptococcus G148 was isolated by molecular cloning. A subclone containing a 1.5-kb insert gave a functional product in Escherichia coli. Protein analysis of affinity-purified polypeptides revealed two gene products, both smaller than protein G spontaneously released from streptococci, but with identical IgG-binding properties. The complete nucleotide sequence of the insert revealed a repeated structure probably evolved through duplications of fragments of different sizes. The deduced amino acid sequence revealed an open reading frame extending throughout the insert, terminating in a TAA stop codon. Analysis of the two gene products by N-terminal amino acid determination suggests that two different TTG codons are recognized in E. coli for initiation of translation to yield the two products. Based on these results several truncated gene constructions were expressed and analysed. The results suggest that the C-terminal part of streptococcal protein G consists of three IgG-binding domains followed by a region which anchors the protein to the cell surface. Structural and functional comparisons with streptococcal M protein and staphylococcal protein A have been made.

The plasmid-encoded lactose genes of the Lactococcus lactis phosphotransferase system encoding Enzyme IIIlac (lacF) and Enzyme IIlac (lacE) have been identified and cloned in Escherichia coli and L. lactis. Nucleotide sequence and transcription analysis showed that these genes are organized into a lactose-inducible operon with the gene order lacF-lacE-lacG-lacX, the latter two genes encoding phospho-beta-galactosidase and a 34-kDa protein with an unknown function, respectively. The lac-operon is immediately followed by an IS element that is homologous to ISS1. Enzyme IIIlac was purified from L. lactis and determination of its NH2-terminal sequence demonstrated that the lacF gene starts with a TTG codon and encodes a 105 amino acid protein (Mr = 11416). Cross-linking studies with the purified enzyme showed that Enzyme IIIlac is active as a trimer. A mutant lacF gene was identified in strain YP2-5 and appeared to encode Enzyme IIIlac containing the missense mutation G18E. The lacF gene could be expressed under control of vector-located promoter sequences resulting in overproduction of Enzyme IIIlac in E. coli and complementation of the L. lactis lacF mutant YP2-5. The deduced amino acid sequence of Enzyme IIlac consists of 586 amino acids (Mr = 61562) and shows the characteristics of a hydrophobic, integral membrane protein. The deduced primary structures of the L. lactis Enzyme IIIlac and Enzyme IIlac are homologous to those of Staphylococcus aureus (72 and 71% identity, respectively) and Lactobacillus casei (48 and 47% identity, respectively). In contrast, the organization of the lactose genes differs significantly between those Gram-positive bacteria. Heterogramic homology in specific domains was observed between the derived amino acid sequences of the lactose-specific enzymes and that of E. coli Enzyme IIIcel and Enzyme IIcel, which suggest a common function in the transport and phosphorylation of these structurally related beta-glucosides.

Tissue transglutaminase (tTG) is a calcium-dependent enzyme that catalyzes the posttranslational modification of proteins by transamidation of specific polypeptide-bound glutamine residues. Previous in vitro studies have demonstrated that the transamidating activity of tTG requires calcium and is inhibited by GTP. To investigate the endogenous regulation of tTG, a quantitative in situ transglutaminase (TG) activity assay was developed. Treatment of human neuroblastoma SH-SY5Y cells with retinoic acid (RA) resulted in a significant increase in tTG levels and in vitro TG activity. In contrast, basal in situ TG activity did not increase concurrently with RA-induced increased tTG levels. However, stimulation of cells with the calcium-mobilizing drug maitotoxin (MTX) resulted in increases in in situ TG activity that correlated (r2 = 0.76) with increased tTG levels. To examine the effects of GTP on in situ TG activity, tiazofurin, a drug that selectively decreases GTP levels, was used. Depletion of GTP resulted in a significant increase in in situ TG activity; however, treatment of SH-SY5Y cells with a combination of MTX and tiazofurin resulted in significantly less in situ TG activity compared with treatment with MTX alone. This raised the possibility of calcium-dependent proteolysis due to the effects of tiazofurin, because in vitro GTP protects tTG against proteolysis by trypsin. Studies with a selective membrane permeable calpain inhibitor indicated that tTG is likely to be an endogenous substrate of calpain, and that depletion of GTP increases tTG degradation after elevation of intracellular calcium levels. TG activity was also increased in response to activation of muscarinic cholinergic receptors, which increases intracellular calcium through inositol 1,4,5-trisphosphate generation. The results of these experiments demonstrate that selective changes in calcium and GTP regulate the activity and levels of tTG in situ.