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ExoI and SbcCD nucleases cooperate with RecBCD enzyme in reckless chromosome degradation in recA mutants of Escherichia coli

Exponentially growing recA mutants of Escherichia coli display pronounced spontaneous DNA degradation that presumably starts at the sites of DNA damage and depends on the 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 sbcB and sbcD genes. The products of these genes are known to code for ExoI and SbcCD nucleases, respectively. Since both sbcB and sbcD mutations are required for full suppression of DNA degradation while individual mutations have only a slight suppressive effect, we infer that ExoI and SbcCD play redundant roles in regulating DNA degradation in recA cells. We suggest that their role might be in processing (blunting) DNA ends thereby producing suitable substrate for RecBCD binding.

Escherichia coli; recA mutants; DNA degradation; ExoI; SbcCD nuclease

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