Abstract
Gloeobacter violaceus is a cyanobacterium that lacks thylakoid membranes, and its complete genome sequence was recently determined. Usually cyanobacterial photosystem (PS) I consists of 11 subunits, however three genes (psaI, psaJ and psaK) were not found in the genome sequence of G. violaceus. We investigated the constitution of the PS I isolated from G. violaceus. We identified eight subunits as predicted from the genome sequence and clarified missing of PsaI, PsaJ and PsaK. We discovered a novel subunit consisting of 35 amino acid residues, and predicted the subunit forms a trans-membrane α-helix. Therefore, we assigned it to a new subunit of G. violaceus and named it PsaZ. Moreover, we found that PsaB has a C-terminal extension with 155 amino acids, and this domain is similar to the peptidoglycan-binding domain of several eubacteria. This is the first demonstration that the functional domain is associated with subunits of photosystems.
