Mechanism of mutation by thymine starvation in Escherichia coli: clues from mutagenic specificity.
AUTOR(ES)
Kunz, B A
RESUMO
To probe the mechanisms of mutagenesis induced by thymine starvation, we examined the mutational specificity of this treatment in strains of Escherichia coli that are wild type (Ung+) or deficient in uracil-DNA-glycosylase (Ung-). An analysis of Ung+ his-4 (ochre) revertants revealed that the majority of induced DNA base substitution events were A:T----G:C transitions. However, characterization of lacI nonsense mutations induced by thymine starvation demonstrated that G:C----A:T transitions and all four possible transversions also occurred. In addition, thymineless episodes led to reversion of the trpE9777 frameshift allele. Although the defect in uracil-DNA-glycosylase did not appear to affect the frequency of total mutations induced in lacI by thymine deprivation, the frequency of nonsense mutations was reduced by 30%, and the spectrum of nonsense mutations was altered. Furthermore, the reversion of trpE9777 was decreased by 90% in the Ung- strain. These findings demonstrate that in E. coli, thymine starvation can induce frameshift mutations and all types of base substitutions. The analysis of mutational specificity indicates that more than a single mechanism is involved in the induction of mutation by thymine depletion. We suggest that deoxyribonucleoside triphosphate pool imbalances, the removal of uracil incorporated into DNA during thymine starvation, and the induction of recA-dependent DNA repair functions all may play a role in thymineless mutagenesis.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=215854Documentos Relacionados
- Control of Cell Division in Escherichia coli: Experiments with Thymine Starvation
- Synchronization of cell division in Escherichia coli by amino acid starvation: strain specificity.
- IS231A from Bacillus thuringiensis is functional in Escherichia coli: transposition and insertion specificity.
- Seryl-tRNA synthetase from Escherichia coli: implication of its N-terminal domain in aminoacylation activity and specificity.
- Loss of Deoxyribonucleic Acid-Thymine During Thymine Starvation of Escherichia coli