Figure 1. A novel role of ATM in prevention of rereplication during unperturbed cell cycle. ATM ensures full activation of Akt, which, in turn, facilitates the expression (or activation) of Skp2 that ubiquitinates Cdt1 for degradation. In the absence of ATM, Akt is not fully activated, resulting in reduction of Skp2 activity and stabilization of Cdt1 during S phase. This predisposes cells to rereplication, one of the major sources for genomic instability.