Abstract
Chloroplast-encoded Ycf4 is essential for the accumulation of Photosystem I (PSI) complex and is a part of large complex (Ycf4 complex) in the green algae Chlamydomonas reinhardtii. The Ycf4 complex was purified and the polypeptide composition was analyzed by immunoblottings and mass spectrometry. In addition to Cop and PsaF, we identified PSI subunits, PsaA, PsaB and PsaD in the purified Ycf4 complex. These polypeptides were easily dissociated from the Ycf4 complex as a chlorophyll-protein complex. Pulse-chase labeling experiments with 35S revealed that the polypeptides on the Ycf4 complex are newly synthesized. These results suggest that an assembly intermediate of PSI complex is loosely bound to the Ycf4 complex. Thus it is conducted that the Ycf4 complex plays a role as a scaffold for PSI complex assembly.
