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Mutation spectra analysis suggests that N‐(2‐chloroethyl)‐N′‐cyclohexyl‐N‐nitrosourea‐induced lesions are subject to transcription‐coupled repair in Escherichia coli
Author(s) -
Ian Raffaella,
Inga Alberto,
LuqueRomero Francisco L.,
Menichini Paola,
Abbondandolo Angelo,
Abril Nieves,
Pueyo Carmen,
Fronza Gilberto
Publication year - 1997
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/(sici)1098-2744(199705)19:1<39::aid-mc6>3.0.co;2-i
Subject(s) - biology , escherichia coli , mutant , genetics , transcription (linguistics) , plasmid , microbiology and biotechnology , mutation , dna repair , dna , nitrosourea , gene , linguistics , philosophy , chemotherapy
To determine the influence of some bacterial DNA report pathways on the mutagenic and the lethal effects of N‐(2‐chloroethyl)‐N′‐cyclohexyl‐N‐nitrosourea (CCNU), pZ189 plasmids treated in vitro with 2 mM CCNU were transfected into Escherichia coli strains with different repair capacities (uvr + ada + ogt + , uvr − ada + ogt + , and uvr − ada − ogt − ). Despite the differences in repair capacities, no statistically significant difference in survival and mutability was observed among the tested strains. One hundred and sixty‐six CCNU‐induced supF mutants were isolated and sequenced. All mutants were characterized by single base‐pair substitutions, most of which (more than 96%) were GC→AT transitions (the mutated G being almost exclusively preceded 5′ by a purine). Mutation distribution was not random. Position 160 (5′‐GGT‐3′, nontranscribed (NT) strand) was a uvr + ada + ogt + ‐specific hot‐spot. Position 123 (5′‐GGG‐3′, NT strand) was a common hot‐spot but significantly more mutable in repair‐proficient strains than in repair‐deficient strains. Conversely, position 168 (5′‐GGA‐3′, transcribed (T) strand) was significantly more mutable in repair‐deficient strains than in repair‐proficient strains. By applying a computer program for comparison of mutational spectra, we found that the uvr + mutational spectrum was significantly different from those obtained in uvr − strains, whereas in the uvr − background, no difference was observed between mutation spectra in ada + ogt + versus ada − ogt − strains. Our results are consistent with the hypothesis that O 6 ‐alkylguanine is responsible for most mutations observed in all strains. The results also indicate that excision repair modulates the distribution of GC→AT transitions. The fact that mutations at G lesions on the T strand were significantly less frequent in uvr + than in uvr − strains suggests that CCNU‐induced premutational lesions are susceptible to strand‐preferential repair in E. coli. Mol. Carcinog. 19:39–45, 1997. © 1997 Wiley‐Liss, Inc.