Nucleotide sequence of cDNA clones encoding the complete precursor for the “10-kDa” polypeptide of photosystem II from spinach

By screening lambda gt11 cDNA expression libraries prepared from poly(A+) RNA of illuminated (4 and 16 h) spinach seedlings (Spinacia oleracea var. Monatol), we have recovered phage containing inserts corresponding to the complete “10-kDa” precursor polypeptide associated with the water oxidizing photosystem II. The amino acid sequence deduced from the nucleotide sequence indicates a polypeptide of 140 amino acid residues (15.0 kDa). The mature protein is predicted to consist of 99 amino acid residues (10.8 kDa). The identity of the recombinant DNAs was established serologically and by determining an N-terminal sequence of 25 amino acid residues from the purified authentic protein. This sequence was found in the cDNA-derived amino acid sequence. In addition, a monospecific antiserum detected the appropriate polypeptides when copy-RNA was translated into protein which was imported into isolated unbroken chloroplasts. The transit sequence (41 amino acid residues; 4.2 kDa) is markedly dissimilar to those of the three extrinsic, luminal photosystem II proteins. Secondary structure prediction suggests a transmembrane arrangement of the 10-kDa polypeptide in the thylakoid membrane, with the N terminus in the thylakoid lumen and a 17-amino acid C-terminal sequence at the outside partitions. This is consistent with biochemical and functional data for the protein. A major transcript of 1.0 kilobases has been observed in polyadenylated RNA.