Mismatch recognition and uracil excision provide complementary paths to both Ig switching and the A/T-focused phase of somatic mutation.
Journal: 2004/December - Molecular Cell
ISSN: 1097-2765
Abstract:
AID-mediated deamination of dC residues within the immunoglobulin locus generates dU:dG lesions whose resolution leads to class-switch recombination and somatic hypermutation. The dU:dG pair is a mismatch and comprises a base foreign to DNA and is, thus, recognized by proteins from both base excision (uracil-DNA glycosylase, UNG) and mismatch recognition (MSH2/MSH6) pathways. Strikingly, while antibody diversification is perturbed by single deficiency in either UNG or MSH2, combined UNG/MSH2 deficiency leads to a total ablation both of switch recombination and of IgV hypermutation at dA:dT pairs. The initiating dU:dG lesions appear not to be recognized and are simply replicated over. The results indicate that the major pathway for switch recombination occurs through uracil excision with mismatch recognition of dU:dG providing a backup; the second phase of hypermutation (essentially introducing mutations solely at dA:dT pairs) is triggered by mismatch recognition of the dU:dG lesion with uracil excision providing a backup.
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