25years on and no end in sight: a perspective on the role of RecG protein.

Robert G Lloyd,Christian J Rudolph

doi:10.1007/s00294-016-0589-z

Robert G Lloyd, Christian J Rudolph

Open Access

https://doi.org/10.1007/s00294-016-0589-z

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Abstract

The RecG protein of Escherichia coli is a double-stranded DNA translocase that unwinds a variety of branched substrates in vitro. Although initially associated with homologous recombination and DNA repair, studies of cells lacking RecG over the past 25 years have led to the suggestion that the protein might be multi-functional and associated with a number of additional cellular processes, including initiation of origin-independent DNA replication, the rescue of stalled or damaged replication forks, replication restart, stationary phase or stress-induced ‘adaptive’ mutations and most recently, naïve adaptation in CRISPR-Cas immunity. Here we discuss the possibility that many of the phenotypes of recG mutant cells that have led to this conclusion may stem from a single defect, namely the failure to prevent re-replication of the chromosome. We also present data indicating that this failure does indeed contribute substantially to the much-reduced recovery of recombinants in conjugational crosses with strains lacking both RecG and the RuvABC Holliday junction resolvase.Electronic supplementary materialThe online version of this article (doi:10.1007/s00294-016-0589-z) contains supplementary material, which is available to authorized users.

Highlights

RecG is a monomeric double-stranded DNA translocase that unwinds a variety of branched DNA molecules in vitro, including Holliday junctions, D-loops, R-loops and various models of replication forks (Lloyd and Sharples 1993; Whitby et al 1993; Vincent et al 1996; Fukuoh et al 1997; McGlynn et al 1997; Whitby and Lloyd 1998; McGlynn and Lloyd 2000; Briggs et al 2004; Rudolph et al 2010b; Manosas et al 2013; Gupta et al 2014; Bianco 2015)
The protein was first described in Escherichia coli, but is present in almost all sequenced species of bacteria (Sharples et al 1999; Rocha et al 2005)
The absence of RecG would stabilise an exchange at a gap, enabling a Holliday junction to be established and covalently sealed in a joint molecule intermediate, an intermediate that we suggest can be resolved only via a canonical resolvase like RuvABC or RusA, as stated above

Summary

Introduction

RecG is a monomeric double-stranded DNA translocase that unwinds a variety of branched DNA molecules in vitro, including Holliday junctions, D-loops, R-loops and various models of replication forks (Lloyd and Sharples 1993; Whitby et al 1993; Vincent et al 1996; Fukuoh et al 1997; McGlynn et al 1997; Whitby and Lloyd 1998; McGlynn and Lloyd 2000; Briggs et al 2004; Rudolph et al 2010b; Manosas et al 2013; Gupta et al 2014; Bianco 2015). Recombination initiated via RecBCD- and RecFOR-mediated loading of RecA might further compound the problem by linking chromosomes and/or partially replicated areas together This scenario certainly fits with the fact that eliminating the helicase activity of PriA needed to initiate overreplication enables irradiated recG cells to recover much more quickly (Rudolph et al 2009b). The absence of RecG would lead to over-replication of DNA via the primosome assembly activity of PriA, triggering and stabilising further (RecBCD-mediated) exchanges that would compromise viability in the absence of RuvABC even if the RecFOR system had been inactivated to reduce or eliminate the initiation of recombination at gaps. Until some proposed roles will have more appeal than others

Conclusions

Findings

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