EVIDENCE FOR BOTH 3'-SINGLE-STRAND AND 5'-SINGLE-STRAND DNA ENDS IN INTERMEDIATES IN CHI-STIMULATED RECOMBINATION IN-VIVO

This paper focuses on elucidation of the structures of intermediates i n recombination stimulated by Chi recombination hotspots in vivo. Sire report that null mutations in genes encoding single-strand exonucleas es of 3' polarity, Exonuclease I (Exo I), of 5' polarity, RecJ, and of both polarities, fro VII, alter the ability of Chi sites to promote r ecombination, and diminish the frequency of recombination. Maximal eff ects occur when single-strand exonucleases of both polarities are elim inated. These data imply that 3' and 5' single-sc-and DNA ends, the su bstrates for these exonucleases, exist in bonafide, product-generating intermediates in Chi-stimulated recombination in vivo. These results also identify three new proteins not known previously to affect RecBCD -mediated recombination.