Document Detail

Targeted disruption of the gene encoding the classical nitroreductase enzyme in Salmonella typhimurium Ames test strains TA1535 and TA1538.
MedLine Citation:
PMID:  9129675     Owner:  NLM     Status:  MEDLINE    
The gene encoding the 'classical nitroreductase' (CNR) of Salmonella typhimurium was disrupted. In this manner, cnr null mutant derivatives of strains TA1535 and TA1538 were constructed, and named YG7131 and YG7127, respectively. In both strain backgrounds, cnr gene disruption reduced nitrofurazone-reductase activity. This reduction almost completely eliminated the nitroreductase activity of strain TA1538. In contrast, the nitroreductase activity of strain TA1535 was much higher than that in TA1538. In this background, cnr gene disruption resulted in a reduction in nitroreductase activity by a similar absolute amount as in TA1538, but representing only about one-quarter of the original activity of TA1535. The results suggest that S. typhimurium has originally at least two distinct nitroreductases, one of which is already deficient in strain TA1538; the CNR is present in both TA1535 and TA1538. Also, these two strains (including their derivatives, TA98 and TA100) are not isogenic with regard to nitroreductase activity. After the introduction of plasmid pKM101, the sensitivities of the strains YG7132 and YG7128, the cnr-null mutants of TA98 and TA100, respectively, against several nitro compounds were compared with those of the conventional cnr-deficient strains TA98NR and TA100NR and the wild-type strains TA98 and TA100. The mutagenicities of 2-nitrofluorene and 1-nitropyrene in YG7132 or TA98NR were ten-fold lower than those of the compounds in TA98. Similarly, the mutagenicity of 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide in strain YG7128 or TA100NR was substantially lower than that of the compound in TA100. However, the mutagenicity of 2-nitronaphthalene in YG7128 was between those observed with TA100 and TA100NR, suggesting that a nitroreductase in S. typhimurium other than CNR is involved in the metabolic activation of this compound. The cnr gene of S. typhimurium positively hybridized with DNA at 13 min on the E. coli chromosome where the nfsB and nfnB genes of E. coli are mapped. These results suggest that the cnr gene of S. typhimurium is a counterpart of the nfsB and nfnB genes of E. coli, and that the newly constructed cnr-deletion strains are useful to assess the role of nitroreductases in the metabolic activation of mutagenic nitro compounds.
M Yamada; J J Espinosa-Aguirre; M Watanabe; K Matsui; T Sofuni; T Nohmi
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Mutation research     Volume:  375     ISSN:  0027-5107     ISO Abbreviation:  Mutat. Res.     Publication Date:  1997 Apr 
Date Detail:
Created Date:  1997-05-15     Completed Date:  1997-05-15     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0400763     Medline TA:  Mutat Res     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  9-17     Citation Subset:  IM    
Division of Genetics and Mutagenesis, National Institute of Health Sciences, Tokyo, Japan.
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MeSH Terms
Blotting, Southern
Chromosome Mapping
Escherichia coli / genetics
In Situ Hybridization
Mutagenicity Tests
Nitro Compounds / pharmacology
Nitroreductases / genetics*,  metabolism
Salmonella typhimurium / drug effects*,  genetics*,  metabolism
Reg. No./Substance:
0/Nitro Compounds; EC 1.7.-/Nitroreductases

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