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Molecular and Cellular Biology, February 2000, p. 1194-1205, Vol. 20, No. 4
Department of Microbiology and Institute of
Cancer Research, Columbia University College of Physicians and
Surgeons, New York, New York 10032
Received 10 June 1999/Returned for modification 20 July
1999/Accepted 19 November 1999
DNA double-strand breaks may be induced by endonucleases, ionizing
radiation, chemical agents, and mechanical forces or by replication of
single-stranded nicked chromosomes. Repair of double-strand breaks can
occur by homologous recombination or by nonhomologous end joining. A
system was developed to measure the efficiency of plasmid gap repair by
homologous recombination using either chromosomal or plasmid templates.
Gap repair was biased toward gene conversion events unassociated with
crossing over using either donor sequence. The dependence of
recombinational gap repair on genes belonging to the RAD52
epistasis group was tested in this system. RAD51,
RAD52, RAD57, and RAD59 were
required for efficient gap repair using either chromosomal or plasmid
donors. No homologous recombination products were recovered from
rad52 mutants, whereas a low level of repair occurred in
the absence of RAD51, RAD57, or
RAD59. These results suggest a minor pathway of strand
invasion that is dependent on RAD52 but not on
RAD51. The residual repair events in rad51
mutants were more frequently associated with crossing over than was
observed in the wild-type strain, suggesting that the mechanisms for
RAD51-dependent and RAD51-independent events are different. Plasmid gap repair was reduced synergistically in
rad51 rad59 double mutants, indicating an important role
for RAD59 in RAD51-independent repair.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
RAD51 Is Required for the Repair of
Plasmid Double-Stranded DNA Gaps from Either Plasmid or
Chromosomal Templates

*
Corresponding author. Mailing address: Department of
Microbiology and Institute of Cancer Research, Columbia University, 701 W. 168th Street, New York, NY 10032. Phone: (212) 305-4793. Fax: (212)
305-1741. E-mail: lss5{at}columbia.edu.
Present address: Department of Nutritional Science, University of
California at Berkeley, Berkeley, CA 94720-3104.
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