In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants brs-1 and brc-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 brc locus controls a dark step while the brs 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 brs-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 brc-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.
GENETIC CONTROL OF CHLOROPHYLL BIOSYNTHESIS IN CHLAMYDOMONAS : Analysis of Mutants at Two Loci Mediating the Conversion of Protoporphyrin-IX to Magnesium Protoporphyrin
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Wei-Yeh Wang, Wenan Lee Wang, John E. Boynton, Nicholas W. Gillham; GENETIC CONTROL OF CHLOROPHYLL BIOSYNTHESIS IN CHLAMYDOMONAS : Analysis of Mutants at Two Loci Mediating the Conversion of Protoporphyrin-IX to Magnesium Protoporphyrin . J Cell Biol 1 December 1974; 63 (3): 806–823. doi: https://doi.org/10.1083/jcb.63.3.806
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