title: The sac mutants of Chlamydomonas reinhardtii reveal transcriptional and posttranscriptional control of cysteine biosynthesis.
abstract: Algae and vascular plants are cysteine (Cys) prototrophs. They are able to import, reduce, and assimilate sulfate into Cys, methionine, and other organic sulfur-containing compounds. Characterization of genes encoding the enzymes required for Cys biosynthesis from the unicellular green alga Chlamydomonas reinhardtii reveals that transcriptional and posttranscriptional mechanisms regulate the pathway. The derived amino acid sequences of the C. reinhardtii genes encoding 5'-adenylylsulfate (APS) reductase and serine (Ser) acetyltransferase are orthologous to sequences from vascular plants. The Cys biosynthetic pathway of C. reinhardtii is regulated by sulfate availability. The steady-state level of transcripts and activity of ATP sulfurylase, APS reductase, Ser acetyltransferase, and O-acetyl-Ser (thiol) lyase increase when cells are deprived of sulfate. The sac1 mutation, which impairs C. reinhardtii ability to acclimate to sulfur-deficient conditions, prevents the increase in accumulation of the transcripts encoding these enzymes and also prevents the increase in activity of all the enzymes except APS reductase. The sac2 mutation, which does not affect accumulation of APS reductase transcripts, blocks the increase in APS reductase activity. These results suggest that APS reductase activity is regulated posttranscriptionally in a SAC2-dependent process.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Cientificas, Universidad de Sevilla, 41092 Sevilla, Spain.
authors.forename: Cristina G
authors.initials: CG
authors.lastname: Ravina
authors.forename: Chwenn-In
authors.initials: CI
authors.lastname: Chang
authors.forename: George P
authors.initials: GP
authors.lastname: Tsakraklides
authors.forename: Jeffery P
authors.initials: JP
authors.lastname: McDermott
authors.forename: Jose M
authors.initials: JM
authors.lastname: Vega
authors.forename: Thomas
authors.initials: T
authors.lastname: Leustek
authors.forename: Cecilia
authors.initials: C
authors.lastname: Gotor
authors.forename: John P
authors.initials: JP
authors.lastname: Davies
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001192:Arylsulfatases / Q000235:genetics / Q000378:metabolism; D019757:Carbon-Oxygen Lyases / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D003545:Cysteine / Q000096:biosynthesis*; D003547:Cysteine Synthase; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D009097:Multienzyme Complexes; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D050862:Oxidoreductases Acting on Sulfur Group Donors; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D051050:Serine O-Acetyltransferase; D013430:Sulfate Adenylyltransferase / Q000235:genetics / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism; D013455:Sulfur / Q000494:pharmacology; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D009097:Multienzyme Complexes; D029701:Saccharomyces cerevisiae Proteins; D013431:Sulfates; D013455:Sulfur; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; C019618:adenylylsulfate reductase; D000123:Acetyltransferases; D051050:Serine O-Acetyltransferase; D003547:Cysteine Synthase; C103381:MET17 protein, S cerevisiae; C018725:O-acetylhomoserine (thiol)-lyase; D013430:Sulfate Adenylyltransferase; D001192:Arylsulfatases; D019757:Carbon-Oxygen Lyases; D003545:Cysteine