title: Sequence analysis and expression of the Salmonella typhimurium asr operon encoding production of hydrogen sulfide from sulfite.
abstract: A chromosomal locus of Salmonella typhimurium which complements S. typhimurium asr (anaerobic sulfite reduction) mutants and confers on Escherichia coli the ability to produce hydrogen sulfide from sulfite was recently cloned (C. J. Huang and E. L. Barrett, J. Bacteriol. 172:4100-4102, 1990). The DNA sequence and the transcription start site have been determined. Analysis of the sequence and gene products revealed a functional operon containing three genes which have been designated asrA, asrB, and asrC, encoding peptides of 40, 31, and 37 kDa, respectively. The predicted amino acid sequences of both asrA and asrC contained arrangements of cysteines characteristic of [4Fe-4S] ferredoxins. The sequence of asrB contained a typical nucleotide-binding region. The sequence of asrC contained, in addition to the ferredoxinlike cysteine clusters, two other cysteine clusters closely resembling the proposed siroheme-binding site in biosynthetic sulfite reductase. Expression of lacZ fused to the asr promoter was repressed by oxygen and induced by sulfite. Analysis of promoter deletions revealed a region specific for sulfite regulation and a second region required for anaerobic expression. Computer-assisted DNA sequence analysis revealed a site just upstream of the first open reading frame which had significant homology to the FNR protein-binding site of E. coli NADH-linked nitrite reductase. However, asr expression by the fusion plasmid was not affected by site-specific mutations within the apparent FNR-binding site.
authors.affiliation: Department of Food Science, University of California, Davis 95616.
authors.forename: C J
authors.initials: CJ
authors.lastname: Huang
authors.forename: E L
authors.initials: EL
authors.lastname: Barrett
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D005288:Ferredoxins / Q000235:genetics; D015870:Gene Expression; D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics; D006862:Hydrogen Sulfide / Q000378:metabolism*; D008969:Molecular Sequence Data; D009251:NADPH-Ferrihemoprotein Reductase; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D009876:Operon / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012313:RNA / Q000032:analysis; D012486:Salmonella typhimurium / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013447:Sulfites / Q000378:metabolism*
chemical_list: D005288:Ferredoxins; D013447:Sulfites; D012313:RNA; D010088:Oxidoreductases; D005993:Glycerolphosphate Dehydrogenase; C028878:ferredoxin-NAD+ reductase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C020155:fumarate reductase (NADH); D009251:NADPH-Ferrihemoprotein Reductase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D006862:Hydrogen Sulfide