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Journal of Bacteriology, November 2006, p. 7562-7571, Vol. 188, No. 21
0021-9193/06/$08.00+0     doi:10.1128/JB.00613-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

sbcB15 and {Delta}sbcB Mutations Activate Two Types of RecF Recombination Pathways in Escherichia coli{triangledown}

Ksenija Zahradka, Sanela Simic, Maja Buljubasic, Mirjana Petranovic, Damir Dermic, and Davor Zahradka*

Division of Molecular Biology, Ruðer Boskovic Institute, Zagreb, Croatia

Received 30 April 2006/ Accepted 14 August 2006

Escherichia coli cells with mutations in recBC genes are defective for the main RecBCD pathway of recombination and have severe reductions in conjugational and transductional recombination, as well as in recombinational repair of double-stranded DNA breaks. This phenotype can be corrected by suppressor mutations in sbcB and sbcC(D) genes, which activate an alternative RecF pathway of recombination. It was previously suggested that sbcB15 and {Delta}sbcB mutations, both of which inactivate exonuclease I, are equally efficient in suppressing the recBC phenotype. In the present work we reexamined the effects of sbcB15 and {Delta}sbcB mutations on DNA repair after UV and {gamma} irradiation, on conjugational recombination, and on the viability of recBC (sbcC) cells. We found that the sbcB15 mutation is a stronger recBC suppressor than {Delta}sbcB, suggesting that some unspecified activity of the mutant SbcB15 protein may be favorable for recombination in the RecF pathway. We also showed that the xonA2 mutation, a member of another class of ExoI mutations, had the same effect on recombination as {Delta}sbcB, suggesting that it is an sbcB null mutation. In addition, we demonstrated that recombination in a recBC sbcB15 sbcC mutant is less affected by recF and recQ mutations than recombination in recBC {Delta}sbcB sbcC and recBC xonA2 sbcC strains is, indicating that SbcB15 alleviates the requirement for the RecFOR complex and RecQ helicase in recombination processes. Our results suggest that two types of sbcB-sensitive RecF pathways can be distinguished in E. coli, one that is activated by the sbcB15 mutation and one that is activated by sbcB null mutations. Possible roles of SbcB15 in recombination reactions in the RecF pathway are discussed.

* Corresponding author. Mailing address: Division of Molecular Biology, Ruðer Boskovic Institute, Bijenicka 54, P.O. Box 180, 10002 Zagreb, Croatia. Phone: 385-1-4560-971. Fax: 385-1-4561-177. E-mail: zahradka{at}irb.hr.

{triangledown} Published ahead of print on 25 August 2006.

Journal of Bacteriology, November 2006, p. 7562-7571, Vol. 188, No. 21
0021-9193/06/$08.00+0     doi:10.1128/JB.00613-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Zahradka, K., Buljubasic, M., Petranovic, M., Zahradka, D. (2009). Roles of ExoI and SbcCD Nucleases in "Reckless" DNA Degradation in recA Mutants of Escherichia coli. J. Bacteriol. 191: 1677-1687 [Abstract] [Full Text]  
  • Larrea, A. A., Pedroso, I. M., Malhotra, A., Myers, R. S. (2008). Identification of two conserved aspartic acid residues required for DNA digestion by a novel thermophilic Exonuclease VII in Thermotoga maritima. Nucleic Acids Res 36: 5992-6003 [Abstract] [Full Text]  
  • Thoms, B., Borchers, I., Wackernagel, W. (2008). Effects of Single-Strand DNases ExoI, RecJ, ExoVII, and SbcCD on Homologous Recombination of recBCD+ Strains of Escherichia coli and Roles of SbcB15 and XonA2 ExoI Mutant Enzymes. J. Bacteriol. 190: 179-192 [Abstract] [Full Text]  


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