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DnaB, DnaD and DnaI proteins are components of the Bacillus subtilis replication restart primosome
C Bruand1, M Farache, S McGovern
1Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas cedex, France. cbruand@toulouse.inra.fr
Insights
Bacillus subtilis priA mutants are deficient in restarting stalled DNA replication forks. New mutations reveal that DnaB, DnaD, and DnaI proteins are crucial for this replication restart process.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The priA gene product in Bacillus subtilis is essential for the restart of stalled chromosomal replication forks.
- PriA is thought to assemble a multiprotein complex, the primosome, to recruit the replication fork helicase.
- Previous work proposed DnaB, DnaD, and DnaI as components of the Bacillus subtilis PriA primosome, but their role in replication restart was unconfirmed.
Purpose of the Study:
- To investigate the involvement of DnaB, DnaD, and DnaI proteins in the replication restart process in Bacillus subtilis.
- To confirm the roles of these proteins as components of the PriA primosome.
- To elucidate the mechanism by which these proteins facilitate replication fork restart.
Main Methods:
- Analysis of Bacillus subtilis priA mutants exhibiting phenotypes indicative of replication restart deficiency.
- Characterization of dnaB mutations that suppress the observed priA mutant phenotypes.
- Biochemical assays to determine the dependency of helicase loading on PriA, DnaD, and DnaI.
Main Results:
- Identification of specific dnaB mutations capable of suppressing the replication restart defect in priA mutants.
- Demonstration that DnaC helicase loading onto single-stranded DNA can occur in a PriA-independent manner.
- Evidence that this PriA-independent helicase loading is dependent on the presence and function of DnaD and DnaI proteins.
Conclusions:
- The findings confirm that DnaB, DnaD, and DnaI are indeed components of the Bacillus subtilis primosome.
- The study establishes the direct participation of DnaB, DnaD, and DnaI in the critical process of replication fork restart.
- This work provides new insights into the molecular mechanisms underlying DNA replication and repair in bacteria.
Abstract:
Phenotypes of Bacillus subtilis priA mutants suggest that they are deficient in the restart of stalled chromosomal replication forks. The presumed activity of PriA in the restart process is to promote the assembly of a multiprotein complex, the primosome, which functions to recruit the replication fork helicase onto the DNA. We have proposed previously that three proteins involved in the initiation of replication at oriC in B. subtilis, DnaB, DnaD and DnaI, are components of the PriA primosome in this bacterium. However, the involvement of these proteins in replication restart has not yet been studied. Here, we describe dnaB mutations that suppress the phenotypes of B. subtilis priA mutants. In a representative mutant, the DnaC helicase is loaded onto single-stranded DNA in a PriA-independent, DnaD- and DnaI-dependent manner. These observations confirm that DnaB, DnaD and DnaI are primosomal proteins in B. subtilis. Moreover, their involvement in the suppression of priA phenotypes shows that they participate in replication fork restart in B. subtilis.