CDK2 and cancer: Considering the presence of the IRO box [11] and of putative Cyclin-binding domains in Irx proteins (http://elm.eu.org), we hypothesize that some Irx mutations may contribute to cancer progression in vertebrates by increasing the activity of the CycE/Cdk2 complex and thus accelerating the G1-S transition, a key step frequently affected in cancer cells [57].