A cDNA clone encoding the complete precursor of the delta subunit of chloroplast ATP synthase has been isolated from a tobacco (Nicotiana tabacum) leaf cDNA library in lambda gt11. The 880 bp insert encodes a polypeptide of 248 amino acid residues, of which 61 residues constitute an N-terminal presequence and 187 residues make up the mature delta subunit. Transcription and translation of the cDNA in vitro produced a protein of 29 kDa which was imported by isolated pea chloroplasts and processed to the mature 20 kDa subunit. The delta subunit precursor was processed to the mature size by a processing peptidase present in pea stromal extracts. Hybridisation of the cDNA to Southern blots of tobacco genomic DNA suggests the presence of two genes in the haploid genome.