Identification of the RecA protein-loading domain of RecBCD enzyme

Genetic recombination in Escherichia coli is stimulated by the recombinatio n hotspot Chi (chi), a regulatory element that modifies the activities of t he RecBCD enzyme and leads to loading of the DNA strand exchange protein, R ecA, onto the chi-containing DNA strand. The RecBC enzyme, which lacks the RecD subunit, loads RecA protein constitutively, in a manner that is indepe ndent of chi. Using a truncated RecBC enzyme lacking the 30 kDa C-terminal domain of the RecB subunit, we show that this domain is necessary for RecA protein-loading. We propose that this domain harbors a site that interacts with RecA protein, recruiting it to single-stranded DNA during unwinding. T his ability of a translocating enzyme to deliver material (RecA protein) to a specific target site (the chi sequence) parallels that of other cellular motor proteins. (C) 2000 Academic Press.