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Eukaryotic Cell, April 2009, p. 487-495, Vol. 8, No. 4
1535-9778/09/$08.00+0     doi:10.1128/EC.00382-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Contrasting Roles of Checkpoint Proteins as Recombination Modulators at Fob1-Ter Complexes with or without Fork Arrest{triangledown}

Bidyut K. Mohanty,* Narendra K. Bairwa, and Deepak Bastia*

Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425

Received 4 December 2008/ Accepted 10 January 2009

The replication terminator protein Fob1 of Saccharomyces cerevisiae specifically interacts with two tandem Ter sites (replication fork barriers) located in the nontranscribed spacer of ribosomal DNA (rDNA) to cause polar fork arrest. The Fob1-Ter complex is multifunctional and controls other DNA transactions such as recombination by multiple mechanisms. Here, we report on the regulatory roles of the checkpoint proteins in the initiation and progression of recombination at Fob1-Ter complexes. The checkpoint adapter proteins Tof1 and Csm3 either positively or negatively controlled recombination depending on whether it was provoked by polar fork arrest or by transcription, respectively. The absolute requirements for these proteins for inducing recombination at an active replication terminus most likely masked their negative modulatory role at a later step of the process. Other checkpoint proteins of the checkpoint adapter/mediator class such as Mrc1 and Rad9, which channel signals from the sensor to the effector kinase, tended to suppress recombination at Fob1-Ter complexes regardless of how it was initiated. We have also discovered that the checkpoint sensor kinase Mec1 and the effector Rad53 were positive modulators of recombination initiated by transcription but had little effect on recombination at Ter. The work also showed that the two pathways were Rad52 dependent but Rad51 independent. Since Ter sites occur in the intergenic spacer of rDNA from yeast to humans, the mechanism is likely to be of widespread occurrence.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425. Phone for Deepak Bastia: (843) 792-0491. Fax: (843) 792-8568. E-mail: bastia{at}musc.edu. Phone for Bidyut K. Mohanty: (843) 792-0281. Fax: (843) 792-8568. E-mail: mohanty{at}musc.edu

{triangledown} Published ahead of print on 20 February 2009.

Eukaryotic Cell, April 2009, p. 487-495, Vol. 8, No. 4
1535-9778/09/$08.00+0     doi:10.1128/EC.00382-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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