title: Genetic control of chlorophyll biosynthesis in Chlamydomonas. Analysis of mutants at two loci mediating the conversion of protoporphyrin-IX to magnesium protoporphyrin.
abstract: In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants br(s)-1 and br(c)-1. Results of experiments with these mutants lead us to postulate that porphyrin biosynthesis branches into light and dark steps between protoporphyrin-IX and magnesium protoporphyrin. We hypothesize that the br(c) locus controls a dark step while the br(s) locus either controls a step in the main pathway before the branch or mediates the preparation of the magnesium ion for its insertion into protoporphyrin-IX. The br(s)-1 mutant is thought to be light sensitive because a block prior to the branch point in the porphyrin pathway prevents chlorophyll formation in either the light or the dark. The br(c)-1 mutant, which also accumulates protoporphyrin in the dark, forms chlorophyll and chloroplast lamellae when transferred to the light, showing that function of the porphyrin pathway is normal in the light.
mesh_terms: D002452:Cell Count; D002696:Chlamydomonas / Q000378:metabolism*; D002734:Chlorophyll / Q000096:biosynthesis*; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D003433:Crosses, Genetic; D003624:Darkness; D004171:Diploidy; D005816:Genetic Complementation Test; D005838:Genotype; D008027:Light; D008274:Magnesium; D008854:Microscopy, Electron; D009154:Mutation; D011166:Porphyrins / Q000378:metabolism*; D013053:Spectrophotometry; D013213:Starch / Q000096:biosynthesis
chemical_list: D011166:Porphyrins; D002734:Chlorophyll; D013213:Starch; D008274:Magnesium