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Molecular and Cellular Biology, September 2009, p. 4742-4756, Vol. 29, No. 17
0270-7306/09/$08.00+0     doi:10.1128/MCB.00471-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Fbh1 Limits Rad51-Dependent Recombination at Blocked Replication Forks{triangledown} ,{ddagger}

Alexander Lorenz,{dagger} Fekret Osman,{dagger} Victoria Folkyte, Sevil Sofueva, and Matthew C. Whitby*

Department of Biochemistry, University of Oxford, South Parks Road, Oxford, United Kingdom

Received 11 April 2009/ Returned for modification 15 May 2009/ Accepted 16 June 2009

Controlling the loading of Rad51 onto DNA is important for governing when and how homologous recombination is used. Here we use a combination of genetic assays and indirect immunofluorescence to show that the F-box DNA helicase (Fbh1) functions in direct opposition to the Rad52 orthologue Rad22 to curb Rad51 loading onto DNA in fission yeast. Surprisingly, this activity is unnecessary for limiting spontaneous direct-repeat recombination. Instead it appears to play an important role in preventing recombination when replication forks are blocked and/or broken. When overexpressed, Fbh1 specifically reduces replication fork block-induced recombination, as well as the number of Rad51 nuclear foci that are induced by replicative stress. These abilities are dependent on its DNA helicase/translocase activity, suggesting that Fbh1 exerts its control on recombination by acting as a Rad51 disruptase. In accord with this, overexpression of Fbh1 also suppresses the high levels of recombinant formation and Rad51 accumulation at a site-specific replication fork barrier in a strain lacking the Rad51 disruptase Srs2. Similarly overexpression of Srs2 suppresses replication fork block-induced gene conversion events in an fbh1{Delta} mutant, although an inability to suppress deletion events suggests that Fbh1 has a distinct functionality, which is not readily substituted by Srs2.

* Corresponding author. Mailing address: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom. Phone: 44-1865-613239. Fax: 44-1865-613343. E-mail: matthew.whitby{at}bioch.ox.ac.uk

{triangledown} Published ahead of print on 22 June 2009.

{ddagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{dagger} These authors contributed equally to this study.

Molecular and Cellular Biology, September 2009, p. 4742-4756, Vol. 29, No. 17
0270-7306/09/$08.00+0     doi:10.1128/MCB.00471-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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