Comparison of yeast and mammalian CDKs. Cells of the budding yeast Saccharomyces cerevisiae contain two cell-cycle-related CDKs that are activated by multiple cyclins - Cdc28 and Pho85. Cdk1 is the mammalian ortholog of Cdc28, whereas Cdk5 is considered to be the Pho85 ortholog. The Cdk4/Cdk6 subfamily is not present in yeast. Kin28, Srb10, Bur1 and Ctk1 are the yeast orthologs of Cdk7, Cdk8, Cdk9 and Cdk12, respectively. The Cdk20 and Cdk11/Cdk10 subfamilies are not represented in yeast. Also indicated is the cyclin partner for the mammalian CDKs. CDK, cyclin-dependent kinase.