Viability of chlamydomonas mutants with amino acid substitutions in the precursor D1 protein at the carboxyl-terminal processing site: An analysis by mixed-culture growth experiments

In order to analyze the influence of amino acid substitutions at the carboxyl-terminal processing site of the D1 precursor protein, mixed-culture growth experiments were conducted for psbA directed mutants of Chlamydomonas reinhardtii. Wild type and D1 mutants were mixed in the same culture and their viability was compared. Replacement of Ser-345 by Gly or Val at the cleavage site markedly affected the relative growth rate of the mutant in the high intensity light, but not in a dim light or the darkness. This was consistent with the previous result obtained by in vitro analysis using substituted carboxyl-terminal oligopeptides as substrates [Taguchi et al. (1995) J. Biol. Chem. 270: 10711]. This is a clear indication that the rate of carboxylterminal processing of the D1 precursor in the photosystem II reaction center is a rate-limiting step for growth under some environmental stress conditions.