What is CDKS?

By definition, a CDK binds a regulatory protein called a cyclin. Without cyclin, CDK has little kinase activity; only the cyclin-CDK complex is an active kinase. CDKs phosphorylate their substrates on serines and threonines, so they are serine-threonine kinases.

To produce two healthy, genetically identical daughter cells, the cell is faced with a number of problems, which can be divided into two groups. On one hand there are the so called completion problems. This concerns the requirement that certain processes in the cell cycle must be finished before others can start. For example mitosis can only begin once all of the DNA has been replicated. The other problem is the alternation problem. The whole cell cycle is an alternation between distinct cell cycle stages, going from G1 to S to G2 to M, and not for example after S (DNA replication) another round of S.

The solution cells use to tackle these problems primarily involves a simple chemical reaction: the transfer of a g phosphate group from ATP to the serine/threonine-hydroxyl group of target proteins which thereby either gain or loose a function. The key enzymes that catalyze this reaction and thus govern cell cycle progress are the cyclin-dependent kinases (CDKs). Different CDKs, control the major steps between different phases of the cell cycle through phosphorylation of cell proteins like histones, cytoskeletal proteins, transcription factors, tumor suppresser genes and others. Hence all external signals related to cell growth and division must eventually regulate the activity of one of the CDKs. This mechanism has been so well conserved during evolution that for example human regulatory proteins can successfully be incorporated and regulate the cell cycle of yeast cells.