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Proc Natl Acad Sci U S A. 1989 Apr;86(8):2627-31.

Identification and purification of a single-stranded-DNA-specific exonuclease encoded by the recJ gene of Escherichia coli.

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  • 1Department of Cell and Molecular Biology, Dana-Farber Cancer Institute, Boston, MA 02115.


The Escherichia coli recJ gene product was overproduced using a plasmid that carries the recJ gene downstream of a strong regulatable promoter and a strong ribosome-binding site. Overexpression of recJ produced a concomitant increase in the levels of single-stranded-DNA-specific nuclease activity present in crude cell extracts. This nuclease activity was purified to homogeneity and found to reside in a 60-kDa polypeptide. This polypeptide was induced with recJ overexpression and had the size and N-terminal amino acid sequence identical to the predicted RecJ protein sequence. The RecJ nuclease degraded linear single-stranded DNA but did not have exonuclease activity on linear double-stranded substrates or endonuclease activity on either single-stranded or double-stranded substrates. The RecJ exonuclease had greater activity on duplex DNA molecules with 5'-rather than 3'-single-stranded tails.

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