ISOLATION OF A PSAF-DEFICIENT MUTANT OF CHLAMYDOMONAS-REINHARDTII - EFFICIENT INTERACTION OF PLASTOCYANIN WITH THE PHOTOSYSTEM-I REACTION-CENTER IS MEDIATED BY THE PSAF SUBUNIT

The PsaF polypeptide of photosystem I (PSI) is located on the lumen si de of the thylakoid membrane and its precise role is not yet fully und erstood. Here we describe the isolation of a psaF-deficient mutant of the green alga Chlamydomonas reinhardtii generated by co-transforming the nuclear genome of the cw15-arg7A strain with two plasmids: one har boring a mutated version of the psaF gene and the other containing the argininosuccinate lyase gene conferring arginine prototrophy. This ps aF mutant still assembles a functional PSI complex and is capable of p hotoautotrophic growth. However, electron transfer from plastocyanin t o P700(+), the oxidized reaction center chlorophyll dimer, is dramatic ally reduced in the mutant, indicating that the PsaF subunit plays an important role in docking plastocyanin to the PSI complex. These resul ts contrast with those obtained previously with a cyanobacterial psaF( -), psaJ(-) double mutant where no phenotype was apparent.