Abstract
Photosystem I (PSI) is a large complex composed of a number of subunits and cofactors. We are interested in the function of the chloroplast-encoded Ycf3 and Ycf4 that are essential for PSI assembly. Here mutants were generated in which 2-9 amino acid residues at N-terminus of Ycf4 have been deleted. Deletion of seven residues (N7) drastically affected PSI complex assembly, indicating the N-terminal sequence has an important role in the stability and function of Ycf4. Separation of PSI complex from the thylakoid extracts from N7 revealed the accumulation of a small amount of unusual PSI complex. According to the apparent size, this PSI complex can be a deteriorated complex or assembly intermediate. We also analyzed the chloroplast mutants in which ycf3 and/or ycf4 had been knocked-out. We will discuss a possible involvement of Ycf4 and Ycf3 in an initial assembly stage of PSI complex.
