The Ca2+/calmodulin-dependent protein kinases (CaM kinases) comprise a structurally related subfamily of serine/threonine kinases which include CaMKI, CaMKII and CaMKIV. CaMKII is an ubiquitously expressed serine/threonine protein kinase that is activated by Ca2+ and calmodulin (CaM) and has been implicated in regulation of the cell cycle and transcription. There are four CaMKII isozymes, designated alpha, beta, gamma and delta, which may or may not be coexpressed in the same tissue type. CaMKIV is stimulated by Ca2+ and CaM but also requires phosphorylation by a CaMK for full activation.