Abstract
The green alga Chlamydomonas reinhardtii has 14 photosystem I (PSI) genes, but PsaN and PsaO have not been detected in the purified PSI preparation. PsaN appears to be an extrinsic protein on the lumenal surface while PsaO with two putative transmembrane helices appears to be intrinsic. Their location in PSI complex is not known because these two subunits are lost in the PSI preparations used for crystal structure analyses. Here we raised antibodies against synthetic oligopeptides corresponding to PsaN and PsaO, respectively. We found that both PsaN and PsaO are stably present in the isolated wild type thylakoids but are easily lost during treatments of the thylakoids with chaotropic agents or mild detergents. It was clearly shown that no PsaN and PsaO accumulate in PSI-deficient mutant, strongly suggesting that they are PSI subunits in Chlamydomonas. We will also discuss the results obtained from otherChlamydomonas PSI mutants.
