Abstract
The chloroplast-encoded polypeptide Ycf4 is essential for assembly of PSI complex in the green alga Chlamydomonas reinhardtii. However, it is unknown how Ycf4 is involved in assembly of PSI complex. To elucidate the function of Ycf4, we generated site-directed mutations in the chloroplast ycf4 gene of C. reinhardtii. We replaced conserved Glu at positions of 179 and 181 from N-terminus by Gln to study the effect of the negative charges on functional assembly of PSI complex. The E179/181Q is unable to grow photosynthetically. The mutant contains Ycf4 like WT, but accumulates only a trace amount of PSI. PSI complexes in the mutant were separated by sucrose density gradient centrifugation into two fractions; the upper fraction corresponds to an unassembled protein while the lower fraction to an assembly intermediate. These mutations seem to inhibit an early step of the assembly of PSI complex.
