Genetic Recombination in Escherichia coli: The Role of Exonuclease I

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RESUMO

The indirect suppression of recB- and recB-recC- mutations by the sbcB- allele is caused by the loss of a nuclease active on denatured DNA. Results from enzyme purifications and studies with a specific antiserum demonstrate that the activity present in sbcB+ strains, and lost in sbcB- strains, is exonuclease I. It is likely that sbcB is the structural gene for exonuclease I. The loss of exonuclease I activity restores the recombination proficiency of Escherichia coli cells that has been lost by mutations in the recB and/or recC genes. This indicates that in the absence of the recB-recC-determined enzyme, exonuclease I prevents recombination. Hypothetical pathways illustrating this conclusion are presented.

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