Mutations in nine chloroplast loci of Chlamydomonas affecting different photosynthetic functions.

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Abstract
Chloroplast components known to be coded by chloroplast DNA include chloroplast rRNAs, tRNAs, and the large subunit of ribulose-bisphosphate carboxylase. Because these components comprise less than 3% of the estimated coding capacity of the chloroplast genome, most chloroplast gene functions have yet to be identified. One approach to this problem is the isolation and characterization of mutations in the chloroplast genome affecting specific photosynthetic functions. Recently it was found that such mutations can be preferentially recovered by using arsenate selection on cells previously grown in 5-fluorodeoxyuridine. Sixteen mutants thus isolated were localized into 9 chloroplast loci, based on their ability to recombine and produce photosynthetically competent progeny. Mutants at 2 loci show the characteristic syndrome of photosynthetic defects that results from a deficiency in chloroplast protein synthesis. These were found to lack chloroplast ribosome monomers. Mutants at 3 loci are missing chlorophyll-protein complex 1 in their thylakoid membranes. Mutants at 3 other loci are deficient in membrane polypeptides known to be associated with the chloroplast coupling factor.