COMPLEMENTATION OF A CHLAMYDOMONAS-REINHARDTII MUTANT DEFECTIVE IN THE NUCLEAR GENE ENCODING THE CHLOROPLAST COUPLING FACTOR-I (CF1) GAMMA-SUBUNIT (ATPC)

Chlamydomonas reinhardtii strain atpC1 is a mutant defective in the nu clear gene that encodes the CF1 ATP synthase gamma-subunit polypeptide . Photoautotrophic growth was restored to atpC1 after it was transform ed with wild-type DNA. Transformed strains were acetate-independent an d arsenate-sensitive, similar in phenotype to the progenitor wild-type strain from which atpC1 was generated. Three transformed strains were examined in detail. Southern blot analyses demonstrated that the tran sformants were complements and not revertants. The transforming DNA in tegrated into the nuclear genome in a nonhomologous manner and at a lo w copy number. Northern blot analyses showed that the gamma-subunit mR NA in the complemented strains was expressed at the same relative leve l as that of wild-type. Western blots of total protein showed that whe reas atpC1 was unable to synthesize any CF1 gamma-subunit, all three c omplemented strains could. Furthermore, the Western blot analyses demo nstrated that the mutation in atpC1 had a pleiotropic effect on the ac cumulation of the CF1 beta-subunit which was relieved upon complementa tion. Cell extracts from atpC1 did not have any CF1-dependent catalyti c activity, whereas extracts from all of the complemented strains and the wild-type strain had identical activities.