Cloning and Sequence Analyses of Five Extrinsic Proteins in Diatom PSII

Abstract

Photosystem II (PSII) particles from a diatom, Chaetoceros gracilis, contains five extrinsic proteins of PsbO, PsbQ', PsbV, PsbU and a novel unknown protein. We cloned the genes encoding PsbO, PsbQ', PsbU, and the novel unknown extrinsic protein by RNA ligase-mediated rapid amplification of cDNA ends (RLMRACE). The deduced proteins consisted of 307 (PsbO), 211 (PsbQ'), 151 (PsbU) and 179 (novel unknown protein) amino acids. All of these proteins contained three characteristic transit peptides, namely, chloroplast ER-signal, chloroplast envelope transfer-signal and thylakoid transfer-signal peptides, indicating that these genes are encoded in the nuclear genome. The mature proteins consist of 248, 155, 93 and 124 amino acids with calculated molecular masses of 26.7, 17.1, 10.1 and 13.3 kDa, respectively. Plastidal DNA fragment containing psbV gene was also isolated using inverse PCR. The deduced protein consists of 163 amino acids which included a characteristic thylakoid transfersignal transit peptide. These results suggest that the novel unknown protein in diatom PSII is located in the lumenal side and probably constitutes, together with the other extrinsic proteins, the functional oxygen-evolving complex.