Cdk1 is a small protein (approximately 34 kilodaltons), and is highly conserved. The human homolog of Cdk1, CDC2, shares approximately 63% amino-acid identity with its yeast homolog. Furthermore, human CDC2 is capable of rescuing fission yeast carrying a cdc2 mutation.[1][9] Cdk1 is comprised mostly by the bare protein kinase motif, which other protein kinases share.