title: Characterization of Chlamydomonas mutants defective in the H subunit of Mg-chelatase.
abstract: Two chlorophyll-deficient mutants of Chlamydomonas reinhardtii, chl1 and brs-1, are light sensitive and, when grown heterotrophically in the dark, accumulate protoporphyrin IX and exhibit yellow/orange pigmentation. The lesions in both mutants were mapped to the gene (CHLH) for the plastid-localized H subunit of the heterotrimeric magnesium chelatase that catalyzes the insertion of magnesium into protoporphyrin IX. The genetic defects in the mutants could be assigned to +1 frameshift mutations in exon 9 (chl1) and exon 10 (brs-1) of the CHLH gene. In both mutants, the H subunit of magnesium chelatase was undetectable, but, as shown for chl1, the steady-state levels of the I and D subunits were unaltered in comparison to wild type. The CHLH gene exhibits marked light inducibility: levels of both the mRNA and the protein product are strongly increased when cultures are shifted from from the dark into the light, suggesting that this protein may play a crucial role in the light regulation of chlorophyll biosynthesis.
authors.affiliation: Institut für Biologie III, Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Chekounova
authors.forename: V
authors.initials: V
authors.lastname: Voronetskaya
authors.forename: J
authors.initials: J
authors.lastname: Papenbrock
authors.forename: B
authors.initials: B
authors.lastname: Grimm
authors.forename: C F
authors.initials: CF
authors.lastname: Beck
mesh_terms: D000595:Amino Acid Sequence; D000622:Aminolevulinic Acid; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015139:Blotting, Southern; D015153:Blotting, Western; D002268:Carboxypeptidases / Q000235:genetics; D002696:Chlamydomonas / Q000201:enzymology*; D002734:Chlorophyll / Q000096:biosynthesis; D002736:Chloroplasts / Q000201:enzymology; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics; D003001:Cloning, Molecular; D017931:DNA Primers / Q000737:chemistry; D016368:Frameshift Mutation; D005656:Fungal Proteins / Q000235:genetics; D005816:Genetic Complementation Test; D008190:Lyases / Q000235:genetics* / Q000378:metabolism; D008780:Methyltransferases / Q000378:metabolism; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011166:Porphyrins / Q000378:metabolism; D011524:Protoporphyrins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D001426:Bacterial Proteins; C066751:CHL1 protein, S cerevisiae; D002868:Chromosomal Proteins, Non-Histone; D017931:DNA Primers; D005656:Fungal Proteins; D011166:Porphyrins; D011524:Protoporphyrins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D002734:Chlorophyll; C011539:protoporphyrinogen; D000622:Aminolevulinic Acid; D008780:Methyltransferases; D002268:Carboxypeptidases; C022633:serine carboxypeptidase; D008190:Lyases; C086788:magnesium chelatase; C100609:ChlH protein, Synechocystis