z-logo
open-access-imgOpen Access
Genetic structure and regulation of the cysG gene in Salmonella typhimurium
Author(s) -
Barry S. Goldman,
John R. Roth
Publication year - 1993
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.175.5.1457-1466.1993
Subject(s) - complementation , auxotrophy , biology , sulfite reductase , mutant , genetics , cistron , gene , regulon , biochemistry , structural gene , nitrite reductase , reductase , enzyme , nitrate reductase
Siroheme, a cofactor of both sulfite and nitrite reductase in Salmonella typhimurium, requires the cysG gene for its synthesis. Three steps are required to synthesize siroheme from uroporphyrinogen III, the last common intermediate in the heme and siroheme pathways. All previously characterized cysG mutants were shown to be defective for the synthesis of cobalamin (B12), which shares a common precursor with siroheme. Since few cysG auxotrophs had been previously analyzed and since there is no evidence of siroheme mutants outside of the cysG region, we sought to expand the analysis of the region by isolating more mutations and studying the transcriptional regulation of the cysG gene using lacZ fusions. We isolated and analyzed 66 cysG auxotrophs. All were defective for both siroheme and cobalamin synthesis. Five exceptional mutants were partially defective for the synthesis of both and appear to be leaky. Complementation tests with tandem duplications suggest that the mutations causing the Cys auxotrophy affect only one cistron. The cysG gene is transcribed in a clockwise direction; this was demonstrated by a method that permits determining the orientation of two genes of unknown orientation provided their relative map order is known. The cysG gene was not part of the cysteine regulon, but had a substantial basal level of expression which was induced fivefold when cells were grown anaerobically on nitrite. Finally, we used Mud-generated duplications to genetically determine the organization of the cysG and nirB genes.

The content you want is available to Zendy users.

Already have an account? Click here to sign in.
Having issues? You can contact us here