May play a role in signal transduction pathways that involve calcium as a second messenger (By similarity). Serine/threonine kinase that phosphorylates histone H3. Confers thermotolerance; involved in the heat-shock-mediated calmodulin-dependent signal transduction leading to the activation of heat-shock transcription factors (HSFs); phosphorylates HSFA1A. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by calcium and calmodulin. Autophosphorylation may play an important role in the regulation of the kinase activity. Binds calmodulin (CaM) in a calcium-dependent manner. Interacts with HSFA1A. There are 3 contiguous domains conserved in the CDPK subfamily: a kinase domain, an autoinhibitory (junction) domain and a calmodulin-like domain. The autoinhibitory domain (390-420) inactivates kinase activity under calcium-free conditions (By similarity). Autophosphorylated. Impaired basal thermotolerance. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.