A STIMULATORY RNA ASSOCIATED WITH RECBCD ENZYME

RecBCD enzyme acts in the major pathway of homologous recombination of linear DNA in Escherichia coli. The enzyme unwinds DNA and is an ATP- dependent double-strand and single-strand exonuclease and a single-str and endonuclease; it acts at Chi recombination hotspots (5'-GCTGGTGG-3 ') to produce a recombinogenic single-stranded DNA 3'-end. We found th at a small RNA with a unique sequence of similar to 24 nt was tightly bound to RecBCD enzyme and co-purified with it. When added to native e nzyme this RNA, but not four others, increased DNA unwinding and Chi n icking activities of the enzyme. In seven similarly active enzyme prep arations the molar ratio of RNA molecules to RecBCD enzyme molecules r anged from 0.2 to <0.008. These results suggest that, although this un ique RNA is not an essential enzyme subunit, it has a biological role in stimulating RecBCD enzyme activity.