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Journal of Bacteriology, September 2008, p. 5995-6001, Vol. 190, No. 17
0021-9193/08/$08.00+0 doi:10.1128/JB.00620-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.


CNRS, Centre de Génétique Moléculaire, UPR 2167, Gif-sur-Yvette F-91198, Université Paris-Sud, Orsay F-91405, and Université Pierre et Marie Curie-Paris 6, Paris F-75005, France
Received 5 May 2008/ Accepted 13 June 2008
Rep and UvrD are two related Escherichia coli helicases, and inactivating both is lethal. Based on the observation that the synthetic lethality of rep and uvrD inactivation is suppressed in the absence of the recombination presynaptic proteins RecF, RecO, or RecR, it was proposed that UvrD is essential in the rep mutant to counteract a deleterious RecFOR-dependent RecA binding. We show here that the synthetic lethality of rep and uvrD mutations is also suppressed by recQ and recJ inactivation but not by rarA inactivation. Furthermore, it is independent of the action of UvrD in nucleotide excision repair and mismatch repair. These observations support the idea that UvrD counteracts a deleterious RecA binding to forks blocked in the rep mutant. An ATPase-deficient mutant of UvrD [uvrD(R284A)] is dominant negative in a rep mutant, but only in the presence of all RecQJFOR proteins, suggesting that the UvrD(R284A) mutant protein is deleterious when it counteracts one of these proteins. In contrast, the uvrD252 mutant (G30D), which exhibits a strongly decreased ATPase activity, is viable in a rep mutant, where it allows replication fork reversal. We conclude that the residual ATPase activity of UvrD252 prevents a negative effect on the viability of the rep mutant and allows UvrD to counteract the action of RecQ, RecJ, and RecFOR at forks blocked in the rep mutant. Models for the action of UvrD at blocked forks are proposed.
Published ahead of print on 20 June 2008.
Present address: Institute of Genetics, The University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, United Kingdom.
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