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Multiple genetic pathways for restarting DNA replication forks in Escherichia coli K-12
1Department of Microbiology, University of Massachusetts, Amherst 01003, USA. sandler@microbio.umass.edu
Insights
Multiple pathways restart DNA replication forks in Escherichia coli. The study reveals synthetic lethality in double mutants, suggesting distinct PriA-dependent and independent replication restart pathways involving key proteins like PriA, PriC, and Rep.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- DNA replication fork restart is crucial for genomic stability in Escherichia coli.
- Primosome assembly proteins (PriA, PriB, PriC, DnaT, DnaC, DnaB, DnaG) are implicated in restarting stalled replication forks.
- Redundancy between priB and priC, and synthetic lethality between priA and rep mutations suggest complex restart mechanisms.
Purpose of the Study:
- To investigate the roles of PriA, PriC, and Rep proteins in DNA replication fork restart pathways.
- To elucidate the genetic interactions and functional relationships between these proteins.
- To determine the mechanism of suppression of replication restart defects by dnaC alleles.
Main Methods:
- Utilized P1 transduction-based viability assays to assess double mutant lethality in Escherichia coli.
- Generated and analyzed double mutants combining priA2::kan with Deltarep::kan or priC303:kan.
- Tested the ability of specific dnaC alleles (dnaC809 and dnaC809,820) to suppress the observed synthetic lethality.
Main Results:
- Demonstrated synthetic lethality between priA2::kan and Deltarep::kan, and between priA2::kan and priC303:kan.
- Identified dnaC809,820 as a suppressor of priA-priC and priA-rep double mutant lethality, while dnaC809 was not.
- Showed that the helicase activity of PriA and Rep is not the sole cause of synthetic lethality in the rep-priA double mutant.
Conclusions:
- Proposed a model with parallel PriA-dependent and PriA-independent pathways for replication restart.
- PriA-dependent pathways require PriA and either PriB or PriC.
- PriA-independent pathways require PriC and Rep, with differential requirements for dnaC suppressor alleles.
Abstract:
In Escherichia coli, the primosome assembly proteins, PriA, PriB, PriC, DnaT, DnaC, DnaB, and DnaG, are thought to help to restart DNA replication forks at recombinational intermediates. Redundant functions between priB and priC and synthetic lethality between priA2::kan and rep3 mutations raise the possibility that there may be multiple pathways for restarting replication forks in vivo. Herein, it is shown that priA2::kan causes synthetic lethality when placed in combination with either Deltarep::kan or priC303:kan. These determinations were made using a nonselective P1 transduction-based viability assay. Two different priA2::kan suppressors (both dnaC alleles) were tested for their ability to rescue the priA-priC and priA-rep double mutant lethality. Only dnaC809,820 (and not dnaC809) could rescue the lethality in each case. Additionally, it was shown that the absence of the 3'-5' helicase activity of both PriA and Rep is not the critical missing function that causes the synthetic lethality in the rep-priA double mutant. One model proposes that replication restart at recombinational intermediates occurs by both PriA-dependent and PriA-independent pathways. The PriA-dependent pathways require at least priA and priB or priC, and the PriA-independent pathway requires at least priC and rep. It is further hypothesized that the dnaC809 suppression of priA2::kan requires priC and rep, whereas dnaC809,820 suppression of priA2::kan does not.