PriB Stimulates PriA Helicase via an Interaction with Single-stranded DNA

Abstract

The frequency with which replication forks break down in all organisms requires that specific mechanisms ensure completion of genome duplication. In Escherichia coli a major pathway for reloading of the replicative apparatus at sites of fork breakdown is dependent on PriA helicase. PriA acts in conjunction with PriB and DnaT to effect loading of the replicative helicase DnaB back onto the lagging strand template, either at stalled fork structures or at recombination intermediates. Here we showed that PriB stimulates PriA helicase, acting to increase the apparent processivity of PriA. This stimulation correlates with the ability of PriB to form a ternary complex with PriA and DNA structures containing single-stranded DNA, suggesting that the known single-stranded DNA binding function of PriB facilitates unwinding by PriA helicase. This enhanced apparent processivity of PriA might play an important role in generating single-stranded DNA at stalled replication forks upon which to load DnaB. However, stimulation of PriA by PriB is not DNA structure-specific, demonstrating that targeting of stalled forks and recombination intermediates during replication restart likely resides with PriA alone. The frequency with which replication forks break down in all organisms requires that specific mechanisms ensure completion of genome duplication. In Escherichia coli a major pathway for reloading of the replicative apparatus at sites of fork breakdown is dependent on PriA helicase. PriA acts in conjunction with PriB and DnaT to effect loading of the replicative helicase DnaB back onto the lagging strand template, either at stalled fork structures or at recombination intermediates. Here we showed that PriB stimulates PriA helicase, acting to increase the apparent processivity of PriA. This stimulation correlates with the ability of PriB to form a ternary complex with PriA and DNA structures containing single-stranded DNA, suggesting that the known single-stranded DNA binding function of PriB facilitates unwinding by PriA helicase. This enhanced apparent processivity of PriA might play an important role in generating single-stranded DNA at stalled replication forks upon which to load DnaB. However, stimulation of PriA by PriB is not DNA structure-specific, demonstrating that targeting of stalled forks and recombination intermediates during replication restart likely resides with PriA alone. Genome duplication is rapid, accurate, and highly processive. However, the DNA replication machinery of all organisms may stall at a frequency that demands the presence of replication repair systems (1Cox M.M. Goodman M.F. Kreuzer K.N. Sherratt D.J. Sandler S.J. Marians K.J. Nature. 2000; 404: 37-41Crossref PubMed Scopus (871) Google Scholar, 2Maisnier-Patin S. Nordstrom K. Dasgupta S. Mol. Microbiol. 2001; 42: 1371-1382Crossref PubMed Scopus (51) Google Scholar). If the replication machinery dissociates from the DNA upon stalling, then the replication machinery must also be reassembled back onto the chromosome (3Kuzminov A. Microbiol. Mol. Biol. Rev. 1999; 63: 751-813Crossref PubMed Google Scholar). In Escherichia coli there are multiple overlapping mechanisms of replication fork reassembly (4Sandler S.J. Genetics. 2000; 155: 487-497PubMed Google Scholar). These reassembly pathways are initiated either by PriC or by PriA helicase (5Heller R.C. Marians K.J. Mol. Cell. 2005; 17: 733-743Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 6Heller R.C. Marians K.J. J. Biol. Chem. 2005; 280: 34143-34151Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar). Cells lacking PriA have low cell viability, reduced recombination, and extreme sensitivity to DNA-damaging agents, demonstrating the frequency with which replication forks stall and also the importance of a PriA-catalyzed mechanism for replication fork reassembly (7Nurse P. Zavitz K.H. Marians K.J. J. Bacteriol. 1991; 173: 6686-6693Crossref PubMed Google Scholar, 8Lee E.H. Kornberg A. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 3029-3032Crossref PubMed Scopus (104) Google Scholar, 9Sandler S.J. Samra H.S. Clark A.J. Genetics. 1996; 143: 5-13Crossref PubMed Google Scholar, 10Kogoma T. Cadwell G.W. Barnard K.G. Asai T. J. Bacteriol. 1996; 178: 1258-1264Crossref PubMed Google Scholar). PriA binds preferentially to three-way branched DNA structures possessing a leading strand in vitro, reflecting the structures thought to occur at recombination intermediates and at some stalled replication forks in vivo (11McGlynn P. Al-Deib A.A. Liu J. Marians K.J. Lloyd R.G. J. Mol. Biol. 1997; 270: 212-221Crossref PubMed Scopus (165) Google Scholar, 12Nurse P. Liu J. Marians K.J. J. Biol. Chem. 1999; 274: 25026-25032Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar). Recognition of such DNA structures is then followed by loading of the replicative helicase, DnaB, back onto the lagging strand template (13Jones J.M. Nakai H. J. Mol. Biol. 1999; 289: 503-516Crossref PubMed Scopus (86) Google Scholar, 14Xu L. Marians K.J. Mol. Cell. 2003; 11: 817-826Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar). DnaB reloading is thought to be the key step in restarting replication, allowing reassembly of both leading and lagging strand polymerases back onto the chromosome and resumption of priming of lagging strand synthesis by DnaG (15Yuzhakov A. Turner J. O'Donnell M. Cell. 1996; 86: 877-886Abstract Full Text Full Text PDF PubMed Scopus (157) Google Scholar). However, PriA cannot facilitate DnaB reloading by itself. Binding of PriA to branched DNA structures possessing a leading strand at the branch point is followed by recruitment of PriB and subsequently of DnaT (14Xu L. Marians K.J. Mol. Cell. 2003; 11: 817-826Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar, 16Liu J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). This PriA-PriB-DnaT complex can then promote reloading of DnaB onto the lagging strand template (5Heller R.C. Marians K.J. Mol. Cell. 2005; 17: 733-743Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar). DnaB can bind to single-stranded DNA (ssDNA) 2The abbreviations used are: ssDNAsingle-stranded DNASSBsingle-stranded binding proteindsDNAdouble-stranded DNA. without the assistance of PriA (17LeBowitz J.H. McMacken R. J. Biol. Chem. 1986; 261: 4738-4748Abstract Full Text PDF PubMed Google Scholar). Indeed, the helicase loader, DnaC, greatly increases binding of ssDNA by DnaB from a DnaB-DnaC complex (18Wahle E. Lasken R.S. Kornberg A. J. Biol. Chem. 1989; 264: 2469-2475Abstract Full Text PDF PubMed Google Scholar, 19Davey M.J. Fang L. McInerney P. Georgescu R.E. O'Donnell M. EMBO J. 2002; 21: 3148-3159Crossref PubMed Scopus (114) Google Scholar). However, two factors present in vivo result in a requirement for the facilitation by other enzymes of loading of DnaB from a DnaB-DnaC complex. First, DnaB cannot bind to ssDNA bound by single-stranded binding protein (SSB) (17LeBowitz J.H. McMacken R. J. Biol. Chem. 1986; 261: 4738-4748Abstract Full Text PDF PubMed Google Scholar). This inhibition can be overcome by the PriA-PriB-DnaT complex allowing loading of DnaB onto an SSB-coated single-stranded lagging strand template (5Heller R.C. Marians K.J. Mol. Cell. 2005; 17: 733-743Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 13Jones J.M. Nakai H. J. Mol. Biol. 1999; 289: 503-516Crossref PubMed Scopus (86) Google Scholar). This inhibition of DnaB loading by SSB and the ability to overcome this inhibition by PriA at branched DNA structures likely provide a regulatory mechanism to ensure DnaB loading occurs only where necessary (20Jones J.M. Nakai H. J. Mol. Biol. 2001; 312: 935-947Crossref PubMed Scopus (46) Google Scholar, 21Cadman C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar). Second, unwinding of the parental strands at a replication fork requires loading of DnaB onto the single-stranded lagging strand template (17LeBowitz J.H. McMacken R. J. Biol. Chem. 1986; 261: 4738-4748Abstract Full Text PDF PubMed Google Scholar, 22Marians K.J. Annu. Rev. Biochem. 1992; 61: 673-719Crossref PubMed Google Scholar). D-loops formed by recombination are thought to be one means by which structures are produced onto which PriA can reload DnaB (11McGlynn P. Al-Deib A.A. Liu J. Marians K.J. Lloyd R.G. J. Mol. Biol. 1997; 270: 212-221Crossref PubMed Scopus (165) Google Scholar, 23Kogoma T. Microbiol. Mol. Biol. Rev. 1997; 61: 212-238Crossref PubMed Scopus (441) Google Scholar), and the strand destined to become the lagging strand template at D-loops is single-stranded. However, at stalled fork structures rather than D-loops the lagging strand template may be double-stranded (24Gregg A.V. McGlynn P. Jaktaji R.P. Lloyd R.G. Mol. Cell. 2002; 9: 241-251Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). Unwinding of this lagging strand duplex may require the 3′- to 5′-helicase function of PriA (13Jones J.M. Nakai H. J. Mol. Biol. 1999; 289: 503-516Crossref PubMed Scopus (86) Google Scholar, 24Gregg A.V. McGlynn P. Jaktaji R.P. Lloyd R.G. Mol. Cell. 2002; 9: 241-251Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). single-stranded DNA single-stranded binding protein double-stranded DNA. Thus PriA can form a complex with PriB and DnaT to promote loading of DnaB onto ssDNA in the presence of SSB. PriA can also unwind any dsDNA present on the lagging strand arm to uncover ssDNA required for binding of DnaB. How these two processes are achieved in the context of the PriA-PriB-DnaT complex is not well PriB to binding of PriA to a by ssDNA of the J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). PriB also with ssDNA or with ssDNA bound by SSB Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google and may also PriA helicase function Marians K.J. J. Biol. Chem. 1989; 264: Full Text PDF PubMed Google Scholar). However, the requirement for PriB in loading of DnaB can be by of DnaT J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). This that PriB facilitates PriA and also that PriA DnaT with the DnaB-DnaC complex during loading of DnaB, PriB acts only to PriA and DnaT binding on the DNA. to the function of PriB during replication restart with the of the of E. coli PriB a with two one in M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, J.H. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, S. T. K. M. T. T. Biochem. Res. 2005; PubMed Scopus Google Scholar). the of PriB with the of SSB. Indeed, the and may have by a duplication L. J. Mol. Microbiol. 2003; PubMed Scopus Google Scholar). PriB and SSB may bind ssDNA in a by of and in PriB in which the of PriB for ssDNA reduced M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). However, the structures of PriB and SSB of this is that there is a on the PriB for with other M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). Thus PriB might function by binding of ssDNA and of such PriA and In this we have that PriB PriA helicase. This stimulation of PriA an increase in apparent The stimulation not DNA structure-specific, suggesting PriB not bind preferentially to branched DNA. PriB formed a complex with PriA in only in the presence of The importance of ssDNA binding in PriB function by the in stimulation of PriA helicase by in PriB which the ability of PriB to form on these that PriB may a processivity for PriA helicase by with both PriA and an may facilitate reloading of the replication machinery by PriA at stalled replication forks by of ssDNA on the lagging strand template for loading of DnaB. DNA by one of which in with at the and by J. Biol. Chem. Full Text PDF PubMed Google Scholar). of the to are and by and duplex by and by and and duplex by and with and and duplex with and with and and duplex with and with and and duplex with and by and and DnaT K.J. PubMed Scopus Google Scholar). SSB C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar). and PriB M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). with a a M. Biochem. PubMed Scopus Google Scholar). DNA Unwinding and Binding at in and DNA used with the of Unwinding at for with SSB PriB to the of PriA to a of and at for a by the of of and and at for The of by in and a DNA binding by of of the DNA with the of in and on for The then in and by and of of by PriA in the presence and of PriB P. A.A. Lloyd R.G. Nucleic Acids Res. 2000; PubMed Scopus Google Scholar), that the used and The of PriA and of PriB used and and the of fork PriA by that PriB with ssDNA Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, J.H. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, S. T. K. M. T. T. Biochem. Res. 2005; PubMed Scopus Google and with PriA bound to ssDNA J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar, Marians K.J. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar), we to the of PriB on PriA helicase function at DNA of PriA to fork a replication fork leading and lagging strand duplex to of PriA helicase is to the lagging strand in such structures (24Gregg A.V. McGlynn P. Jaktaji R.P. Lloyd R.G. Mol. Cell. 2002; 9: 241-251Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar), PriA processivity of or C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar, R.S. Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Marians K.J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus (85) Google Scholar). of unwinding of fork by PriA is with this However, of PriB containing PriA and fork that unwinding of the lagging strand duplex by to This unwinding required PriA suggesting that PriB unwinding by PriA of the demonstrating a binding for and helicase on DNA can also unwind duplex DNA (11McGlynn P. Al-Deib A.A. Liu J. Marians K.J. Lloyd R.G. J. Mol. Biol. 1997; 270: 212-221Crossref PubMed Scopus (165) Google Scholar, 12Nurse P. Liu J. Marians K.J. J. Biol. Chem. 1999; 274: 25026-25032Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar). The ability of PriB to unwinding by PriA of a duplex containing the duplex of fork of PriB PriA-catalyzed unwinding of this to the fork Thus stimulation of PriA helicase by PriB not DNA may be mechanisms for the reloading of DnaB at stalled forks and recombination intermediates (4Sandler S.J. Genetics. 2000; 155: 487-497PubMed Google Scholar, S.J. Genetics. 2005; PubMed Scopus Google Scholar). such mechanism requires and a mechanism PriC only (5Heller R.C. Marians K.J. Mol. Cell. 2005; 17: 733-743Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar). the ability of PriC and DnaT to PriA-catalyzed unwinding of fork PriB unwinding of the lagging strand by PriA stimulation upon of PriC or DnaT and of PriC or DnaT to containing both PriA and PriB effect on the of unwinding of fork not that stimulation of PriA helicase is specific to PriB to helicase on a of DNA not is a low processivity DNA helicase is at the lagging strand of stalled replication forks to effect reloading of DnaB R.C. Marians K.J. J. Biol. Chem. 2005; 280: 34143-34151Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar). Thus PriB stimulation of replication restart is to PriA. that in vivo in the presence of the effect of SSB on PriB stimulation of PriA helicase also SSB is known to PriA helicase on branched DNA and on DNA SSB PriA helicase (20Jones J.M. Nakai H. J. Mol. Biol. 2001; 312: 935-947Crossref PubMed Scopus (46) Google Scholar, 21Cadman C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar). fork the presence of either PriB or SSB unwinding of the lagging strand duplex by PriA and of both PriB and SSB to PriA to a of stimulation of unwinding of fork than with either PriB or SSB only The stimulation by PriB and SSB to be duplex PriB PriA and However, SSB unwinding of duplex by PriA only and and SSB also the stimulation of PriA by PriB and and Thus PriB PriA helicase on branched DNA in the presence of SSB. However, SSB unwinding of DNA by PriA of the presence of PriB the of the in that PriB might increase the apparent processivity of PriA helicase, the processivity of PriA at branched and DNA DNA structures containing lagging strand of there a in PriA-catalyzed unwinding upon the lagging strand duplex from to unwinding of and of PriA processivity on the duplex DNA structures a However, the of unwinding on the with the DNA and unwinding of the not increase upon from to suggesting that binding of PriA not the at PriA If binding of PriA to the not then of unwinding of with forks be to the of PriA helicase on duplex with DNA. The ability of PriB to PriA-catalyzed unwinding of DNA and stimulation of unwinding of the lagging strand duplex by of PriB with duplex of and However, the of unwinding of the lagging strand duplex with PriA in the of PriB that any stimulation and The of PriA reduced to and unwinding of the duplex by PriB and the effect with the stimulation with lagging strand of that of PriB to of the ability of PriA to unwind lagging strand of or of PriA-catalyzed unwinding of of in branched and DNA in a of the of PriB on the duplex structures stimulation of PriA-catalyzed unwinding of all from to and The stimulation by PriB of PriA-catalyzed unwinding of the duplex with that for the duplex in the context of fork This in stimulation correlates with the processivity of PriA on duplex to the DNA However, the of stimulation of PriA helicase by PriB on some on duplex of PriB and stimulation of PriA-catalyzed unwinding of the and the of stimulation with the processivity of PriA the duplex from to Thus PriB the apparent processivity of PriA helicase. this increase apparent on both branched and DNA the that stimulation of PriA by PriB not DNA PriB a with PriA on DNA to form a complex with PriA on the a single-stranded DNA Marians K.J. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). PriB also to bind ssDNA Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google Scholar). used to the DNA for of a complex. PriA bound to fork a lagging strand to form a complex complex PriB not form a complex with fork the of ssDNA in fork of PriB to PriA and fork not to of other than that with PriA only to fork that the lagging strand arm single-stranded. PriA bound to fork complex PriB not form a complex with fork However, of PriB to fork and PriA result in of a complex complex the of complex on both PriA and we that this complex a of both with fork at all of PriB only a complex and not This of complex and that complex PriA and a PriB also with a The of PriA for ssDNA to DNA P. Liu J. Marians K.J. J. Biol. Chem. 1999; 274: 25026-25032Abstract Full Text Full Text PDF PubMed Scopus (85) Google a PriA than that used with the DNA structures in this PriA a complex with this complex complex with the with PriB only However, in the presence of both PriA and a complex complex that of a complex requires that the DNA ssDNA not require that the DNA be we a complex PriA and a we to a complex upon of PriB to this complex not Thus of a complex required and of of a complex on DNA containing ssDNA that PriB might PriA on such PriA-catalyzed on fork with and without However, in the of by PriA in the presence and of PriB be of PriA that PriB effect on the or with to not However, PriB the with to DNA from to for fork not PriA and PriB form a complex on DNA structures containing this effect on by PriA. of PriA by PriB Binding of PriB to the binding of ssDNA by PriB a role in stimulation of PriA helicase. PriB with reduced for ssDNA M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google for stimulation of PriA helicase on fork which a lagging strand and of stimulation PriB on fork PriB reduced stimulation of PriA at low PriB at PriB The two and PriB reduced stimulation of PriA at all and not of stimulation fork possessing a lagging strand to the lagging strand of fork not The apparent for the the and and the and for a in the of PriA M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). The reduced of the not to upon the ability of PriB to PriA helicase. These ssDNA binding by PriB a major role in stimulation of PriA helicase. However, the greatly reduced stimulation of PriA by PriB with the apparent of this PriB for ssDNA M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). for this apparent is that of PriB with PriA bound to DNA might increase the of PriB the DNA a increase in PriB might the of reduced for ssDNA by the PriB in the of PriA. the ability of the PriB to form with PriA bound to DNA PriB in the presence of PriA formed a complex with fork with a reduced with the complex formed with PriA and fork only and that the and PriB the ability to form a complex. is that the for complex to a correlates with the of for ssDNA M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). The of complex might a for the the complex. In complex with PriB However, some of complex in the presence of PriB suggesting that a ternary complex formed during the PriB and PriB also formed low of a complex with fork in the of PriA in likely reflecting low binding of PriB to DNA in the of PriA. Thus the stimulation of PriA by PriB with the ability of PriB to form a complex. of this ternary complex with the of PriB for Binding of ssDNA by PriB a complex to be required for stimulation of PriA helicase. PriB is known to bind ssDNA Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M. J.M. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, J.H. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar), to with PriA to form a complex Marians K.J. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar), and to facilitate PriA and DnaT J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). The that PriB also stimulates PriA-catalyzed unwinding of duplex DNA This stimulation in an apparent increase in the processivity of PriA helicase and complex required for stimulation of PriA by PriB and and of this ternary complex required DNA possessing ssDNA How might PriB the apparent processivity of PriA protein of binding increases the apparent processivity of PriA by two First, the of SSB with PriA and stimulation of PriA-catalyzed duplex unwinding C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar). Second, SSB binding of ssDNA intermediates of PriA-catalyzed unwinding increases the apparent processivity of PriA C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar, R.S. Kornberg A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Marians K.J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus (85) Google Scholar). of intermediates of DNA unwinding by strand is known to the apparent processivity of E. Rev. 2003; PubMed Scopus Google Scholar), upon of the helicase and allowing binding of a helicase to of the of PriB are K.H. Marians K.J. J. Biol. Chem. 1991; Full Text PDF PubMed Google Scholar), this not form a in the of in SSB S. K. Sci. 2004; PubMed Scopus Google Scholar). the PriB might not a protein is to that PriB increases the apparent processivity of PriA by of of intermediates. In this the processivity of PriA result in of PriA to completion of PriB bound to the intermediates and a PriA to bind to the DNA and a unwinding to unwinding of the This that PriB bound to ssDNA in the of PriA and that is this of PriB that the apparent processivity of PriA. However, the of PriB for ssDNA is enhanced the DNA is bound also by PriA and The of this is that PriB might not with ssDNA upon of PriB of ssDNA in a to SSB. PriB and ssDNA and PriB and PriA might be for stimulation of PriA helicase. This is by the of PriB to low processivity helicase in replication R.C. Marians K.J. J. Biol. Chem. 2005; 280: 34143-34151Abstract Full Text Full Text PDF PubMed Scopus (73) Google not a ternary complex might be achieved PriB with PriA to effect a in PriA. a might the of of PriA from DNA during the unwinding that PriB binding of PriA to DNA J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google also upon of PriA from DNA of PriA with PriB bound to ssDNA by PriA might the PriA the DNA an to an increase in the of of PriA with intermediates in an apparent increase in However, the of bound single-stranded enhanced upon of PriB to PriA and such on the DNA containing ssDNA and of PriB that for ssDNA cannot with PriA are to the mechanism of stimulation of PriA. of ssDNA for of a complex This that stimulation of PriA helicase by PriB might occur only unwinding of any duplex lagging strand DNA by PriA ssDNA for PriB this not the of PriA stimulation that any stimulation of PriA helicase at forks a dsDNA lagging strand arm must occur of unwinding by PriA. targeting of stalled forks for replication fork reloading to with the DNA binding of PriA rather than This by the of DNA of PriB stimulation of PriA and If PriB role in the DNA of replication might the function of stimulation of PriA helicase be in The stimulation of PriA by SSB to ensure that ssDNA is on the lagging strand template of stalled forks for loading of DnaB to occur C.J. McGlynn P. Nucleic Acids Res. 2004; 32: 6378-6387Crossref PubMed Scopus (133) Google Scholar). PriB stimulation of PriA might a However, have that the helicase function of PriA is important for not replication restart S.J. Mol. Microbiol. 2001; PubMed Scopus Google Scholar). might be that the pathway replication from stalled to a requirement for PriA helicase the lagging strand arm is the pathway might restart from both forks and restarting replication from D-loops is an PriA helicase not be be required is restart from a fork with a duplex lagging strand This PriA helicase to be in the context of a to restart replication from the stimulation of PriA helicase be to the ability of PriB to PriA and DnaT J. Nurse P. Marians K.J. J. Biol. Chem. 1996; 271: 15656-15661Abstract Full Text Full Text PDF PubMed Scopus (71) Google for the increase in apparent processivity of PriA a in PriA. is that any in PriA both an PriA and DnaT and increases the processivity of PriA. The stimulation of PriA helicase by both PriB and SSB a point helicase in rather low suggesting that the of unwinding is in The of PriA that of complex in which of play a role in the of the be the in vivo function of from in of in Marians for the and