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J. Biol. Chem., Vol. 283, Issue 36, 24909-24921, September 5, 2008

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Defective Dissociation of a "Slow" RecA Mutant Protein Imparts an Escherichia coli Growth Defect^*

From the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706-1544

The RecA and some related proteins possess a simple motif, called (KR)X(KR), that (in RecA) consists of two lysine residues at positions 248 and 250 at the subunit-subunit interface. This study and previous work implicate this RecA motif in the following: (a) catalyzing ATP hydrolysis in trans,(b) coordinating the ATP hydrolytic cycles of adjacent subunits, (c) governing the rate of ATP hydrolysis, and (d) coupling the ATP hydrolysis to work (in this case DNA strand exchange). The conservative K250R mutation leaves RecA nucleoprotein filament formation largely intact. However, ATP hydrolysis is slowed to less than 15% of the wild-type rate. DNA strand exchange is also slowed commensurate with the rate of ATP hydrolysis. The results reinforce the idea of a tight coupling between ATP hydrolysis and DNA strand exchange. When a plasmid-borne RecA K250R protein is expressed in a cell otherwise lacking RecA protein, the growth of the cells is severely curtailed. The slow growth defect is alleviated in cells lacking RecFOR function, suggesting that the defect reflects loading of RecA at stalled replication forks. Suppressors occur as recA gene alterations, and their properties indicate that limited dissociation by RecA K250R confers the slow growth phenotype. Overall, the results suggest that recombinational DNA repair is a common occurrence in cells. RecA protein plays a sufficiently intimate role in the bacterial cell cycle that its properties can limit the growth rate of a bacterial culture.

Received for publication, May 22, 2008 , and in revised form, July 3, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grant GM32335. 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.

¹ To whom correspondence should be addressed: Dept. of Biochemistry, University of Wisconsin, 433 Babcock Dr., Madison, WI 53706-1544. Tel.: 608-262-1181; Fax: 608-265-2603; E-mail: cox{at}biochem.wisc.edu.

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