Any of a family of proteins that act as serine/threonine kinases and are vital components of many intracellular signalling pathways. Inactive PKC is located in the cytoplasm, where it is activated by diacylglycerol (DAG) or other controllers (such as elevated levels of intracellular calcium ions), causing it to migrate to the plasma membrane. Here it phosphorylates serine and threonine residues on target proteins, which translocate to the nucleus and regulate gene transcription. PKC signalling pathways via metabotropic receptors are crucial, for example, in the modulation of ion channel activity in nerve cells by such neurotransmitters as noradrenaline and GABA and also play a role in memory and learning.