Characterization of the cys gene locus from Allochromatium vinosum indicates an unusual sulfate assimilation pathway.
Homologues of the genes cysB, cysI, cysH, cysD, cysN, and selD were identified in the genome of the phototrophic purple sulfur bacterium Allochromatium vinosum (formerly Chromatium vinosum). On the basis of amino acid comparisons these genes encode a ferredoxin-dependent siroheme-sulfite reductase (CysI), a plant-type assimilatory APS reductase without thioredoxin domain (CysH), the two different subunits of heterodimeric ATP sulfurylase (CysDN), a transcriptional regulator (CysB) and a selenophosphate synthase (SelD). cysIHDN appear to form an operon and are preceded by cysB which is transcribed in the opposite direction. SelD is situated downstream of cysN and transcribed divergently to cysIHDN. The lack of a gene for APS kinase and presence of a gene for an assimilatory APS reductase implies that assimilatory sulfate reduction in A. vinosum proceeds along the pathway suggested for higher plants without intermediary formation of PAPS. Two completely separate pathways involving specialized enzymes are used for assimilatory sulfate reduction and dissimilatory sulfur oxidation in A. vinosum. The presence of cysB indicates that the genes for assimilatory sulfate reduction are expressed only in the absence of reduced sulfur compounds.
Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany.
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D000595:Amino Acid Sequence; D001419:Bacteria / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D029721:Drosophila Proteins; D015964:Gene Expression Regulation, Bacterial; D050885:Hydrogensulfite Reductase; D008969:Molecular Sequence Data; D005810:Multigene Family; D009876:Operon; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000378:metabolism; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013430:Sulfate Adenylyltransferase / Q000235:genetics / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*; D015238:Sulfotransferases / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; C062886:CysB protein, Bacteria; D029721:Drosophila Proteins; D013431:Sulfates; D050862:Oxidoreductases Acting on Sulfur Group Donors; C022321:PAPS sulfotransferase; D050885:Hydrogensulfite Reductase; D010770:Phosphotransferases; D013430:Sulfate Adenylyltransferase; C062762:selenophosphate synthetase; D015238:Sulfotransferases