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. Source: Reactome Protein phosphorylation sites were added based on information from PhosphoSitePlus (R), www.phosphosite.org. Proteins on this pathway have targeted assays available via the [https://assays.cancer.gov/available_assays?wp_id=WP45 CPTAC Assay Portal] a31 d30 parentid=P24941; parentsymbol=CDK2; site=VEKIGEGtyGVVykA; position=thr14; sitegrpid=447738; ptm=p; direction=d parentid=P24941; parentsymbol=CDK2; site=EKIGEGtyGVVykAR; position=tyr15; sitegrpid=447740; ptm=p; direction=d parentid=P06400; parentsymbol=RB1; site=AVIPINGsPRtPRRG; position=ser249; sitegrpid=447975; ptm=p; direction=d parentid=P06400; parentsymbol=RB1; site=AVIPINGsPRtPRRG; position=ser249; sitegrpid=447975; ptm=p; direction=d parentid=P46527; parentsymbol=CDKN1B; site=NAGsVEQtPKKPGLR; position=thr187; sitegrpid=447875; ptm=p; direction=d Maeda Gadd45 regulates G2/m arrest cell cycle checkpoint pathway PW:0000094 Pathway Ontology G1/S DNA damage checkpoint pathway PW:0000095 Pathway Ontology 25514926 PubMed PhosphoSitePlus, 2014: mutations, PTMs and recalibrations. Nucleic Acids Res 2015 Hornbeck PV Zhang B Murray B Kornhauser JM Latham V Skrzypek E 12164919 PubMed GADD45 regulates G2/M arrest, DNA repair, and cell death in keratinocytes following ultraviolet exposure. J Invest Dermatol 2002 Maeda T Hanna AN Sim AB Chua PP Chong MT Tron VA