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Mutagen stability of alkylation-sensitive mutants of Bacillus subtilis
Abstract:
A series of mutations of Bacillus subtilis, conferring sensitivity to methyl methanesulfonate (MMS), were transferred by transformation to a suppressible his(-) stock. The introduction of certain sensitivity mutations prevented the ultraviolet- or MMS-induced, but not the spontaneous, reversion of his(-) to his(+). Not all sensitivity mutations led to this resistance to mutagenesis; a strain with altered deoxyribonucleic acid (DNA) polymerase activity behaved almost normally with respect to its mutagen response, as did an excision-defective, ultraviolet-sensitive strain used as a control. One of the mutagen-stable strains responded to mutagenesis with nitrosomethylguanidine; another appeared stable even to this mutagen. All mutagen-stable strains had DNA polymerase and DNA ligase activity.
Insights
Certain mutations in Bacillus subtilis can block DNA repair, preventing mutagenesis from agents like UV light or MMS. However, some strains with DNA polymerase and ligase activity remained mutable, indicating complex DNA repair pathways.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacillus subtilis is a model organism for studying DNA repair mechanisms.
- Mutations conferring sensitivity to methyl methanesulfonate (MMS) were investigated.
- Understanding DNA repair is crucial for comprehending mutagenesis and genetic stability.
Purpose of the Study:
- To investigate the relationship between DNA repair mutations and resistance to mutagenesis.
- To identify specific mutations affecting DNA repair pathways in Bacillus subtilis.
- To characterize the role of DNA polymerase and DNA ligase in mutagen stability.
Main Methods:
- Mutagenesis screening using methyl methanesulfonate (MMS).
- Genetic transformation to transfer mutations into a suppressible his(-) stock.
- Assessing spontaneous and induced reversion rates (his(-) to his(+)).
- Evaluating mutagen response to ultraviolet (UV) light and nitrosomethylguanidine.
Main Results:
- Certain MMS-sensitivity mutations prevented UV- or MMS-induced mutagenesis but not spontaneous reversion.
- Altered DNA polymerase activity did not confer mutagen stability.
- An excision-defective, UV-sensitive control strain showed normal mutagen response.
- Mutagen-stable strains possessed both DNA polymerase and DNA ligase activity.
- One stable strain responded to nitrosomethylguanidine, another was stable to it.
Conclusions:
- DNA repair pathways in Bacillus subtilis are complex and involve multiple components.
- Specific mutations can confer resistance to mutagenesis by interfering with DNA repair.
- DNA polymerase and DNA ligase activities are associated with mutagen stability in Bacillus subtilis.