DNA sequence analysis of spontaneous lacI-d mutations in O6-alkylguanine-DNA alkyltransferase-proficient and -deficient Escherichia coli.
Mutagenesis
; 13(4): 367-73, 1998 Jul.
Article
en En
| MEDLINE
| ID: mdl-9717173
ABSTRACT
Spontaneous mutagenesis in O6-alkylguanine-DNA alkyltransferase-proficient and -deficient (ada ogt mutants) Escherichia coli was studied in two ways in bacteria growing in nonselective liquid medium and in bacteria resting on selective agar plates. ATase mutants showed similar spontaneous mutation rates as ATase proficient bacteria during growth phase; an excess of mutants arising in nondividing cells. The resting-associated mutagenesis in ada + ogt + uvr- bacteria was biphasic; the high sensitive range being triggered beyond the first 6 days after plating. Contrarily, spontaneous Lacc mutants from ada- ogt- uvr- cells steadily increased over the 8 day period of plate incubation. These results suggested that, in the absence of nucleotide excision repair, the repair by both the Ada and the Ogt ATases is not saturated until the cells have been resting for 6 days. The spontaneous LacI-d mutation spectrum of ada + ogt + uvr- bacteria growing in non-selective liquid medium served as a baseline to determine the mutation events increased in the ATase-deficient derivative upon prolonged incubation on selective plates. The percentage of GC-->AT transitions, presumably driven by unrepaired O6-alkylguanine lesions, was increased at the expense of other mutation types. GC-->AT transitions accumulated with a pronounced 5'PuG bias, suggesting that the endogenous metabolite(s) responsible for this mutation class is an SN1 type alkylating compound(s). Accordingly, the site distribution of GC-->AT transitions in nondividing ATase defective bacteria showed similarities with the spectra induced by alkylnitrosoureas, particularly with those generating bulky alkylated DNA adducts.
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Banco de datos:
MEDLINE
Asunto principal:
Proteínas Represoras
/
Proteínas Bacterianas
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ADN Helicasas
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O(6)-Metilguanina-ADN Metiltransferasa
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Proteínas de Escherichia coli
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Escherichia coli
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Mutación
Idioma:
En
Año:
1998
Tipo del documento:
Article