| Abstract
| - The RecA protein of Escherichia coli isrequired for homologous genetic recombination andinduction of the SOS regulon. In order for RecA protein tofunction in these two roles, a nucleosidetriphosphate cofactor, usually ATP or dATP, is required. We haveexamined the ability of UTP to substitutefor (r,d)ATP as nucleoside triphosphate cofactor. We havefound that although UTP is hydrolyzed byRecA protein in the presence of long DNA molecules, it is nothydrolyzed in reactions in which thecofactors are oligodeoxyribonucleotides less than ∼50 nt in length.We show that UTP can efficientlysubstitute for ATP as nucleoside triphosphate cofactor for the DNAstrand exchange reaction in vitro.The RecA1332 protein (Cys129 → Met), which was originally shownto be defective for homologousrecombination in vivo, is able to perform DNA strand exchange in vitrowith ATP, but is unable to do sowith UTP. These results suggest that UTP may be a cofactor for DNAstrand exchange in vivo. Theinability of RecA protein to hydrolyze UTP witholigodeoxyribonucleotides as cofactor and the ability ofRecA to utilize UTP as cofactor in DNA strand exchange suggest aseparation of the functions of RecAprotein into those that require exclusively ATP and those which canutilize additional nucleosidetriphosphate cofactors.
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