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Journal of Bacteriology, March 2009, p. 1677-1687, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01877-07
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Roles of ExoI and SbcCD Nucleases in "Reckless" DNA Degradation in recA Mutants of Escherichia coli{triangledown}

Ksenija Zahradka, Maja Buljubasic, Mirjana Petranovic,{dagger} and Davor Zahradka*

Laboratory for Molecular Microbiology, Division of Molecular Biology, Ruðer Boskovic Institute, Zagreb, Croatia

Received 29 November 2007/ Accepted 4 December 2008

Exponentially growing recA mutant cells of Escherichia coli display pronounced DNA degradation that starts at the sites of DNA damage and depends on RecBCD nuclease (ExoV) activity. As a consequence of this "reckless" DNA degradation, populations of recA mutants contain a large proportion of anucleate cells. We have found that both DNA degradation and anucleate-cell production are efficiently suppressed by mutations in the xonA (sbcB) and sbcD genes. The suppressive effects of these mutations were observed in normally grown, as well as in UV-irradiated, recA cells. The products of the xonA and sbcD genes are known to code for the ExoI and SbcCD nucleases, respectively. Since both xonA and sbcD mutations are required for strong suppression of DNA degradation while individual mutations have only a weak suppressive effect, we infer that ExoI and SbcCD play partially redundant roles in regulating DNA degradation in recA cells. We suggest that their roles might be in processing (blunting) DNA ends, thereby producing suitable substrates for RecBCD binding.

* Corresponding author. Mailing address: Laboratory for Molecular Microbiology, 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 12 December 2008.

{dagger} Mirjana Petranovic passed away on 14 October 2008, after a long and courageous struggle with severe illness. She was a great teacher and a true friend to all of us.

Journal of Bacteriology, March 2009, p. 1677-1687, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01877-07
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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