Abstract
The assembly of PSI complex is a multi-step process, which is assisted by several factors because this complex consists many subunits and cofactors. Among these factors is the chloroplast-encoded Ycf4 that is a part of a large complex. To address the assembly step(s) in which Ycf4 is involved, site-directed mutations were introduced into the ycf4 gene of the green alga Chlamydomonas reinhardtii by chloroplast transformation. We focused on two Glu residues at the position of 179 and 181 that are highly conserved among oxygenic photosynthetic organisms. Substitution of these residues with Gln (E179/181Q) impaired the assembly of PSI complex while substitution of one of the Glu residues did not significantly affect the process. Characterization of PSI proteins in the E179/181Q revealed that the assembly is terminated at an integration of reaction center proteins, which indicates that Ycf4 is involved in an early step of the assembly process.
