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Localization of the plasmid (pKM101) gene(s) involved in recA+lexA+-dependent mutagenesis
Abstract:
Twenty Tn5 insertion mutants of the drug resistance plasmid pKM101 have been isolated that are unable to enhance mutagenesis with ultraviolet (UV) irradiation or methyl methanesulfonate. By restriction mapping, the Tn5 insertion in each of these pKM101 mutants was shown to be within a 1.9 kb region of the plasmid genome. We have termed this segment of the pKM101 map the muc (mutagenesis: UV and chemical) gene(s). Characterization of these mutants indicated that any Tn5 insertion within the muc gene(s) abolished the ability of pKM101 to: (a) enhance spontaneous, UV and chemical mutagenesis, (b) increase host survival following UV-irradiation, (c) increase the survival of UV-irradiated phage plated on irradiated or unirradiated cells, and (d) suppress the repair and mutagenesis deficiencies of a umuC- mutant. Possible models to explain the role of the pKM101 muc gene(s) in mutagenesis and repair are discussed.
Insights
Researchers identified the muc genes on the pKM101 plasmid, which are essential for enhancing mutagenesis and host survival after UV irradiation or chemical exposure. Disruption of these genes impairs DNA repair and mutagenesis.
Area of Science:
- Molecular Biology
- Microbial Genetics
- DNA Repair Mechanisms
Background:
- The pKM101 plasmid is known to enhance mutagenesis and survival following DNA damage.
- The specific genetic elements responsible for these effects were not fully characterized.
Purpose of the Study:
- To identify and characterize the genes on the pKM101 plasmid involved in enhancing mutagenesis and DNA repair.
- To elucidate the role of these genes in response to UV irradiation and chemical mutagens.
Main Methods:
- Isolation and characterization of Tn5 insertion mutants of the pKM101 plasmid.
- Restriction mapping to localize Tn5 insertions.
- Phenotypic analysis of mutants for mutagenesis enhancement, host survival, and suppression of umuC- deficiencies.
Main Results:
- Twenty Tn5 insertion mutants unable to enhance mutagenesis were isolated.
- All insertions were localized to a 1.9 kb region, designated the muc (mutagenesis: UV and chemical) genes.
- Disruption of muc genes abolished pKM101's ability to enhance spontaneous, UV, and chemical mutagenesis, increase host survival post-UV, enhance phage survival, and suppress umuC- mutant deficiencies.
Conclusions:
- The pKM101 muc genes are critical for mediating enhanced mutagenesis and DNA repair.
- These genes play a significant role in cellular responses to DNA-damaging agents like UV and methyl methanesulfonate.
- The muc genes likely interact with or are part of the bacterial SOS response pathway.