The disclosure provides compositions and methods for increasing efficiency of Cas9-mediated target DNA modification. Specifically, the disclosure provides compositions and methods for carrying out site-directed modification of a target DNA, the methods comprising contacting the target DNA with: a) a complex comprising a Cas9 polypeptide and a guide RNA, and b) a Rad51 polypeptide. The site-directed modification of a target DNA can be carried out in a living cell in vitro, in a living cell in vivo, or in a cell-free system in vitro.La présente invention concerne des compositions et des méthodes qui permettent d'augmenter l'efficacité de modification d'ADN cible à médiation assurée par Cas9.