Site-specific mutagenesis of the D1 subunit of photosystem II in wild-type Chlamydomonas.

The structure and functional mode of photosystem II reaction center protein D1 can be studied by analyzing the effects of amino acid substitutions within the binding niche for QB, the second stable electron acceptor of photosystem II, on herbicide binding. Here we report on site-directed mutagenesis of the psbA gene coding for the D1 protein in the unicellular alga Chlamydomonas reinhardtii. The chloroplasts of wild-type cells were transformed using the particle gun. The plasmids introduced carried an in vitro mutated fragment of the psbA gene. We obtained a double mutant with replacements of amino acids 264 and 266 and a triple mutant having an additional substitution in position 259. The sensitivities of both mutants toward several types of herbicides are given and compared with those of a mutant having only a substitution at position 264.