Cyclin dependent kinase 5 (Cdk5) is a key regulator of cell cycle progression in neuronal differentiation that physically associates with and is activated by the neuron-specific protein p35. CDK5RAP1 (CDK5 regulatory subunit-associated protein 1) specifically inhibits Cdk5 activation by p35 through formation of a dimer that inhibits kinase activity. CDK5RAP2, also known as Centrosome-associated protein 215, is a 1893 amino acid centrosomal protein that regulates activity of CDK5 through complex formation with CDK5RAP1. Expressed in placenta, liver, pancreas, heart, skeletal muscle, lung, brain and kidney, CDK5RAP2 associates with centrosomes throughout the cell cycle. Mutations in the gene encoding CDK5RAP2 results in primary microencephaly autosomal recessive type 3, which is characterized by markedly reduced head size, brain weight and significant neurological deficits. There are four isoforms of CDK5RAP2 that are produced as a result of alternative splicing events.