Regulates the G1/S phase transition of the cell cycle by binding and activating CDK1 and CDK2 (PubMed:12972555). Contributes to CDK2 activation without promoting CDK2 phosphorylation, by inducing a conformation change of the CDK2 T-loop that obstructs the substrate- binding cleft prior to kinase activation (PubMed:28666995). Mediates cell survival during the DNA damage process through activation of CDK2 (PubMed:12839962). {ECO:0000269|PubMed:11980914, ECO:0000269|PubMed:12839962, ECO:0000269|PubMed:12972555, ECO:0000269|PubMed:28666995}. This is the function of Ensembl gene identifier ENSG00000163806 (SPDYA, speedy/RINGO cell cycle regulator family member A).