Abstract
RecG is a DNA translocase that helps to maintain genomic integrity. Initial studies suggested a role in promoting recombination, a possibility consistent with synergism between recG and ruv null alleles and reinforced when the protein was shown to unwind Holliday junctions. In this article we describe novel suppressors of recG and show that the pathology seen without RecG is suppressed on reducing or eliminating PriB, a component of the PriA system for replisome assembly and replication restart. Suppression is conditional, depending on additional mutations that modify ribosomal subunit S6 or one of three subunits of RNA polymerase. The latter suppress phenotypes associated with deletion of priB, enabling the deletion to suppress recG. They include alleles likely to disrupt interactions with transcription anti-terminator, NusA. Deleting priB has a different effect in ruv strains. It provokes abortive recombination and compromises DNA repair in a manner consistent with PriB being required to limit exposure of recombinogenic ssDNA. This synergism is reduced by the RNA polymerase mutations identified. Taken together, the results reveal that RecG curbs a potentially negative effect of proteins that direct replication fork assembly at sites removed from the normal origin, a facility needed to resolve conflicts between replication and transcription.
Highlights
The assembly of replication fork complexes at sites removed from the normal chromosomal origin plays a vitalAccepted 20 August, 2012. *For correspondence
Initial studies suggested a role in promoting recombination, a possibility consistent with synergism between recG and ruv null alleles and reinforced when the protein was shown to unwind Holliday junctions
In this article we describe novel suppressors of recG and show that the pathology seen without RecG is suppressed on reducing or eliminating PriB, a component of the PriA system for replisome assembly and replication restart
Summary
The assembly of replication fork complexes at sites removed from the normal chromosomal origin plays a vitalAccepted 20 August, 2012. *For correspondence. PriA is a DNA helicase with a 3′–5′ polarity of strand translocation It has a strong affinity for three-strand junctions, enabling it to target a D-loop intermediate in recombination, or a fork structure, with high specificity (McGlynn et al, 1997; Nurse et al, 1999). PriB is related to SSB and binds with high affinity to ssDNA It stabilizes a PriA–DNA complex, stimulates PriA helicase activity and facilitates binding of DnaT. As with the PriA system, PriC facilitates DnaB loading in the presence of SSB It can do so in vitro without the aid of other proteins (Heller and Marians, 2005), but may require the 3′–5′ helicase activity of either Rep or PriA to do so efficiently in vivo (Sandler, 2000; Mahdi et al, 2006; Gabbai and Marians, 2010)
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