G1 to S cell cycle control (Homo sapiens)

In the G1 phase there are two types of DNA damage responses, the p53-dependent and the p53-independent pathways. The p53-dependent responses inhibit CDKs through the up-regulation of genes encoding CKIs mediated by the p53 protein, whereas the p53-independent mechanisms inhibit CDKs through the inhibitory T14Y15 phosphorylation of Cdk2. Failure of DNA damage checkpoints in G1 leads to mutagenic replication of damaged templates and other replication defects.

GenMAPP notes 

Adapted from http://www.genomeknowledge.org/, and Maeda et al. Journal of Invest Dermatol. 2002. 119:22-26.