CDK5RAP3 (CDK5 regulatory subunit-associated protein 3) was identified as a protein that associates with the activating subunit of Cdk5, p25NCK5A. Cdk5 is a brain specific cyclin-dependent kinase important to mammalian brain development; however CDK5RAP3 appears to be widely expressed in human tissues. CDK5RAP3 appears to exhibit functions that extend beyond its association with Cdk5. CDK5RAP3 is involved in modulating the G2/M DNA damage checkpoint and can associate with and regulate the Cdk1-cyclin B1 complex. CDK5RAP3 has also been demonstrated to interact with and regulate the tumor suppressor ARF (alternative reading frame) to further play a role in cell cycle progression.