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J. Biol. Chem., Vol. 279, Issue 50, 52024-52032, December 10, 2004

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DNA Helicase Activity of the RecD Protein from Deinococcus radiodurans^*

Jianlei Wang and Douglas A. Julin

From the Department of Chemistry & Biochemistry, University of Maryland, College Park, Maryland 20742

The bacterium Deinococcus radiodurans is extremely resistant to high levels of DNA-damaging agents, including gamma rays and ultraviolet light that can lead to double-stranded DNA breaks. Surprisingly, the organism does not appear to have a RecBCD enzyme, an enzyme that is critical for double-strand break repair in many other bacteria. The D. radiodurans genome does encode a protein whose closest characterized homologues are RecD subunits of RecBCD enzymes in other bacteria. We have purified this novel D. radiodurans RecD protein and characterized its biochemical activities. The D. radiodurans RecD protein is a DNA helicase that unwinds short (20 base pairs) DNA duplexes with either a 5'-single-stranded tail or a forked end, but not blunt-ended or 3'-tailed duplexes. Duplexes with 10–12 nucleotide (nt) 5'-tails are good unwinding substrates and are bound tightly, while DNA with shorter tails (4–8 nt) are poor unwinding substrates and are bound much less tightly. The RecD protein is much less efficient at unwinding slightly longer substrates (52 or 76 base pairs, with 12 nt 5'-tails). Unwinding of the longer substrates is stimulated somewhat (4–5-fold) by the single-stranded DNA-binding protein from D. radiodurans. These results show that the D. radiodurans RecD protein is a DNA helicase with 5'-3' polarity and low processivity.

Received for publication, July 29, 2004 , and in revised form, October 4, 2004.

^* This work was supported by Grant GM39777 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 301-405-1821; Fax: 301-314-9121; E-mail: dj13{at}umail.umd.edu.

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