NUCLEAR MUTANTS OF CHLAMYDOMONAS-REINHARDTII DEFECTIVE IN THE BIOGENESIS OF THE CYTOCHROME B(6)F COMPLEX

The random integration of transforming DNA into the nuclear genome of Chlamydomonas has been employed as an insertional mutagen to generate a collection of photosynthetic mutants that display abnormal steady-st ate fluorescence levels and an acetate-requiring phenotype. Electron p aramagnetic resonance spectroscopy was then used to identify those mut ants that specifically lack a functional cytochrome b(6)f complex. Our analysis of RNA and protein synthesis in five of these mutants reveal s four separate phenotypes. One mutant fails to accumulate transcript for cytochrome f, whilst a second displays a severely reduced accumula tion of the cytochrome b, transcript. Two other mutants appear to be a ffected in the insertion of the haem co-factor into cytochrome b,. The fifth mutant displays no detectable defect in the synthesis of any of the known subunits of the complex. Genetic analysis of the mutants de monstrates that in three cases, the mutant phenotype co-segregates wit h the introduced DNA. For the mutant affected in the accumulation of t he cytochrome f transcript, we have used the introduced DNA as a tag t o isolate the wild-type version of the affected gene.