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Journal of Bacteriology, August 2002, p. 4141-4147, Vol. 184, No. 15
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.15.4141-4147.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

The RuvABC Resolvase Is Indispensable for Recombinational Repair in sbcB15 Mutants of Escherichia coli

Davor Zahradka,^* Ksenija Zahradka, Mirjana Petranovi, Damir ermi, and Krunoslav Bri-Kosti

Department of Molecular Genetics, Ruder Bokovi Institute, Zagreb, Croatia

Received 29 October 2001/ Accepted 8 May 2002

The RuvABC proteins of Escherichia coli play an important role in the processing of Holliday junctions during homologous recombination and recombinational repair. Mutations in the ruv genes have a moderate effect on recombination and repair in wild-type strains but confer pronounced recombination deficiency and extreme sensitivity to DNA-damaging agents in a recBC sbcBC background. Genetic analysis presented in this work revealed that the ruvABC mutation causes an identical DNA repair defect in UV-irradiated recBC sbcBC, sbcBC, and sbcB strains, indicating that the sbcB mutation alone is responsible for the extreme UV sensitivity of recBC sbcBC ruv derivatives. In experiments with gamma irradiation and in conjugational crosses, however, sbcBC ruvABC and sbcB ruvABC mutants displayed higher recombination proficiency than the recBC sbcBC ruvABC strain. The frequency of conjugational recombination observed with the sbcB ruvABC strain was quite similar to that of the ruvABC single mutant, indicating that the sbcB mutation does not increase the requirement for RuvABC in a recombinational process starting from preexisting DNA ends. The differences between the results obtained in three experimental systems used suggest that in UV-irradiated cells, the RuvABC complex might act in an early stage of recombinational repair. The results of this work are discussed in the context of recent recombination models which propose the participation of RuvABC proteins in the processing of Holliday junctions made from stalled replication forks. We suggest that the mutant SbcB protein stabilizes these junctions and makes their processing highly dependent on RuvABC resolvase.

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* Corresponding author. Mailing address: Department of Molecular Genetics, Ruer Bokovi Institute, Bijenika 54, P.O. Box 180, 10002 Zagreb, Croatia. Phone: 385-1-4560-971. Fax: 385-1-4561-177. E-mail: zahradka{at}rudjer.irb.hr.

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Journal of Bacteriology, August 2002, p. 4141-4147, Vol. 184, No. 15
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.15.4141-4147.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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