The cobT gene of Salmonella typhimurium encodes the NaMN: 5,6-dimethylbenzimidazole phosphoribosyltransferase responsible for the synthesis of N1-(5-phospho-alpha-D-ribosyl)-5,6-dimethylbenzimidazole, an intermediate in the synthesis of the nucleotide loop of cobalamin.
AUTOR(ES)
Trzebiatowski, J R
RESUMO
We present in vitro evidence which demonstrates that CobT is the nicotinate nucleotide:5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (EC 2.4.2.21) that catalyzes the synthesis of N1-(5-phospho-alpha-D-ribosyl)-5,6-dimethylbenzimidazole, a biosynthetic intermediate of the pathway that assembles the nucleotide loop of cobalamin in Salmonella typhimurium. Mutants previously isolated as DMB auxotrophs are shown by physical and genetic mapping studies and complementation studies to carry lesions in cobT. Explanations for this unexpected phenotype of cobT mutants are discussed. The expected nucleotide loop assembly phenotype of cobT mutants can be observed only in a specific genetic background, i.e., cobB deficient, an observation that is consistent with the existence of an alternative CobT function (G. A. O'Toole, M. R. Rondon, and J. C. Escalante-Semerena, J. Bacteriol. 175:3317-3326, 1993). Computer analysis of CobT homologs showed that at the amino acid level, enteric CobT proteins were 80% identical whereas Pseudomonas denitrificans and Rhizobium meliloti CobT proteins were 95% identical. Interestingly, the degree of identity between enteric and nonenteric CobT homologs was only 30%. The same pattern of homologies was reported for the S. typhimurium CobA, Escherichia coli BtuR, and P. denitrificans CobO proteins (S.-J. Suh and J.C. Escalante-Semerena, Gene 129:93-97, 1993), suggesting evolutionary divergence between the cob genes found in the enteric bacteria E. coli and S. typhimurium and those found in P. denitrificans and R. meliloti.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=205545Documentos Relacionados
- THE EFFECT OF 5,6-DIMETHYLBENZIMIDAZOLE AND RELATED COMPOUNDS ON THE GROWTH OF LACTOBACILLUS LACTIS DORNER1
- Analysis of mutants of Salmonella typhimurium defective in the synthesis of the nucleotide loop of cobalamin.
- The end of the cob operon: evidence that the last gene (cobT) catalyzes synthesis of the lower ligand of vitamin B12, dimethylbenzimidazole.
- Genetic analysis, nucleotide sequence, and products of two Pseudomonas denitrificans cob genes encoding nicotinate-nucleotide: dimethylbenzimidazole phosphoribosyltransferase and cobalamin (5'-phosphate) synthase.
- In vitro synthesis of the nucleotide loop of cobalamin by Salmonella typhimurium enzymes