Homology-arm length of donor DNA affects the impact of Msh2 loss on homologous recombination-mediated gene targeting.

Efficient targeted integration (TI) of homologous donor DNA is crucial for precise genome editing. Although mismatch repair (MMR) is known to suppress TI as well as homologous recombination (HR) when sequence divergence is present, it remains controversial as to whether MMR affects TI of isogenic donor DNA. In this study, we investigated whether and how the MMR protein Msh2 affects TI of isogenic donor DNA. We found that HR-dependent TI is suppressed by Msh2 only when a homology arm of donor DNA is as short as 1.7 kb. In contrast, single-strand annealing-mediated TI, which is cell cycle-independent and becomes prominent when HR or non-homologous end joining is inactivated, is weakly but constantly affected by Msh2 irrespective of the size of homology arms. Our results reveal a previously unrecognized type of HR suppression by Msh2 and provide implications for precise genome editing using short-arm donor DNA vectors.