Cell Cycle Control Part I cdc related kinases

The central and rate-limiting function in the cell cycle control is performed by p34cdc2 kinase in lower organisms, and by p33cdk2 and p34cdc2 in higher organisms. This control is highly conserved throughout evolution. The activities of these kinases are regulated by phosphorylation and dephosphorylation as well as interaction with the cyclins during different phases of the cell cycle. The product p34cdc2 regulates both G1/S and G2/M transitions in yeast. While it is generally accepted that cdk2 plays a critical direct role at G1/S transition in mammalian cells. However, the functions of human cdc2-related kinases, other than cdk2 and cdk3, remain obscure. Certainly the active kinase forms phosphorylate a large number of proteins and enzymes involved in nuclear and nucleolar structures, cellular cytoskeletal systems, and DNA spindle fiber associated relations during mitosis. All of these are logical targets for cell cycle control, or at least its last stage, mitosis.