Protein kinase C is an important target enzyme for lipid second messengers. Recent developments have focused on the tertiary structure analysis of domains present in protein kinase C and in combination with functional approaches such as mutagenesis and domain expression have generated a detailed understanding of the modular mechanism by which lipids cause activation. This provides a reference for the study of the protein kinase C-related kinases, a recently identified new class of kinases that are highly related to protein kinase C in their catalytic characteristics but have distinct regulatory features