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Functional characterization of two SOS-regulated genes involved in mitomycin C resistance in Caulobacter crescentus

Carina O Lopes-Kulishev1, Ingrid R Alves1, Estela Y Valencia1

  • 1Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil.

DNA Repair
|July 12, 2015
PubMed

Insights

Two genes, mmcA and mmcB, defend against mitomycin C (MMC) DNA damage in Caulobacter crescentus. MmcB specifically aids MMC-induced mutagenesis via translesion synthesis, suggesting it

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • The SOS response is a conserved bacterial mechanism for DNA damage repair.
  • Several genes in Caulobacter crescentus's SOS regulon have undetermined functions.
  • DNA damaging agents like mitomycin C (MMC) trigger cellular stress responses.

Purpose of the Study:

  • To investigate the roles of two novel genes, mmcA and mmcB, in the SOS response of Caulobacter crescentus.
  • To determine the specific DNA damaging agents against which mmcA and mmcB provide defense.
  • To elucidate the mechanism of action for MmcA and MmcB in DNA repair and mutagenesis.

Main Methods:

  • Assessing bacterial survival and mutagenesis following exposure to various DNA damaging agents (MMC, UVC, MMS, H2O2).
  • Performing epistasis analysis to determine genetic interactions between mmcB and known DNA repair genes (imuC).
  • Analyzing the SOS induction of the imuABC operon in response to MMC.
  • Utilizing structural analysis of MmcB homologs.

Main Results:

  • MmcA and MmcB are specifically involved in defense against MMC-induced DNA damage.
  • MmcA functions independently of known DNA repair pathways.
  • MmcB acts in the same pathway as imuC and is crucial for MMC-induced mutagenesis, but not UV-induced mutagenesis.
  • The imuABC operon is properly induced in mmcB mutants, indicating MmcB's role is downstream of induction.
  • MmcB is proposed to be an endonuclease involved in translesion synthesis (TLS) of MMC-induced lesions.

Conclusions:

  • MmcA and MmcB represent novel components of the bacterial SOS response, with specific roles in combating MMC-induced DNA damage.
  • MmcB plays a critical role in facilitating translesion synthesis-dependent repair of MMC-induced DNA damage.
  • MmcB is hypothesized to function as an endonuclease, processing DNA lesions to enable ImuABC-mediated TLS.
Keywords:
Caulobacter crescentusEndonucleasesMitomycin CSOS responseTranslesion synthesisdnaE2imuC

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