<unk> s <unk> s) are a family of sugar kinases first discovered for their role in regulating the cell cycle. They are also involved in regulating transcription, mRNA processing, and the differentiation of nerve cells. They are present in all known eukaryotes, and their regulatory function in the cell cycle has been evolutionarily conserved. In fact, yeast cells can proliferate normally when their<unk>  gene has been replaced with the homologous human gene.<unk> s are relatively small proteins, with molecular weights ranging from 34 to 40 kDa, and contain little more than the kinase domain. By definition, a<unk>  binds a regulatory protein called a<unk> . Without<unk> ,<unk>  has little kinase activity; only the<unk> -CDK complex is an active kinase.<unk> s phosphorylate their substrates on serines and threonines, so they are serine-threonine kinases. The consensus sequence for the phosphorylation site in the amino acid sequence of a<unk>  substrate is [S/T*]PX[K/R], where S/T* is the phosphorylated serine or threonine, P is proline, X is any amino acid, K is lysine, and R is arginine.
Cyclin-dependent kinase
Janus kinase
GTPase activating protein
Rho GTPase
Mitogen-activated protein kinase
Adenylate cyclase
Serine/threonine-specific protein kinase
Receptor tyrosine kinase