Molecular and Cellular Biology, July 2000, p. 4948-4957, Vol. 20, No. 13
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Copyright © 2000, American Society for Microbiology. All rights reserved.


Department of Genetics, University of Washington, Seattle, Washington 98195,1 and Department of Biochemistry and Molecular Biology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey, Pennsylvania 170332
Received 14 February 2000/Accepted 21 March 2000
In the ribosomal DNA of Saccharomyces cerevisiae, sequences in the nontranscribed spacer 3' of the 35S ribosomal RNA gene are important to the polar arrest of replication forks at a site called the replication fork barrier (RFB) and also to the cis-acting, mitotic hyperrecombination site called HOT1. We have found that the RFB and HOT1 activity share some but not all of their essential sequences. Many of the mutations that reduce HOT1 recombination also decrease or eliminate fork arrest at one of two closely spaced RFB sites, RFB1 and RFB2. A simple model for the juxtaposition of RFB and HOT1 sequences is that the breakage of strands in replication forks arrested at RFB stimulates recombination. Contrary to this model, we show here that HOT1-stimulated recombination does not require the arrest of forks at the RFB. Therefore, while HOT1 activity is independent of replication fork arrest, HOT1 and RFB require some common sequences, suggesting the existence of a common trans-acting factor(s).
Present address: Rosetta Inpharmatics, Kirkland, WA 98034.
Present address: The Whitehead Institute, Cambridge, MA 02142.
§
Present address: Department of Molecular, Cellular and
Developmental Biology, University of Colorado, Boulder, CO 80309.
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