Import and processing of the precursor form of the gamma subunit of the chloroplast ATP synthase from tobacco

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Abstract
A cDNA clone encoding the complete precursor of the γ subunit of chloroplast ATP synthase has been isolated from a tobacco (Nicotiana tabacum) leaf cDNA library in λgt11. The 1.4 kb insert encodes a polypeptide of 377 amino acid residues, of which 55 residues constitute an N-terminal presequence and 322 residues make up the mature γ subunit. Hybridisation of the cDNA to Southern blots of tobacco genomic DNA indicates the presence of two genes in the haploid genome. Transcription and translation of the cDNA in vitro produced a protein of 41 kDa which was imported by isolated pea chloroplasts and processed to the mature 36 kDa subunit. The γ subunit precursor was processed to the mature size by a processing peptidase of 180 kDa present in pea stromal extracts.