Cre-ad infection of Xrcc1flox/flox myoblasts at 3 and 6 h post-low-serum exposure led to a complete block in differentiation, similar to the results obtained for shRNA targeting of the Xrcc1 gene and Cre-mediated deletion of Xrcc1 in cycling myoblasts (Figure 5d). Here, XRCC1 is linked to infection.