Plastocyanin is encoded by a single-copy gene in the pea haploid genome

Abstract

cDNA clones for pea plastocyanin were isolated from a pea leaf cDNA library screened with a (32)P-labelled mixed oligonucleotide probe predicted from part of the N-terminal amino acid sequence of pea plastocyanin. The six cDNA clones isolated were found to be identical in the regions in which they overlapped. A Southern blot of restricted pea DNA probed with one of these cDNA clones showed the pea plastocyanin gene to exist as a single copy in the haploid genome. A pea genomic library in λEMBL3 screened with the same cDNA clone gave three positive plaques which contained identical 16 kbp Bam HI fragments. A single uninterrupted plastocyanin gene was located near the middle of the fragment and was characterised by DNA sequencing. The derived amino acid sequence indicates that the plastocyanin precursor consists of 168 amino acid residues including a presequence of 69 amino acid residues. The transcription initiation site was located by S1 nuclease mapping approximately 50 bp upstream of the translation initiation site. A sequence similar to a consensus light-responsive element found in a large number of phytochrome-dependent light-inducible genes is located just upstream of the TATA box. A cluster of direct repeats containing potential Z-DNA-forming elements occurs 600-750 bp upstream of the transcription initiation site.