Protein kinase C (PKC) is a family of serine-threonine kinases that regulate a broad spectrum of cellular functions. The family is composed of nine genes that express structurally related phospholipid-dependent kinases with distinct means of regulation and tissue distribution. Based on their structures and sensitivities to Ca2+ and diacylglycerol (DAG), they have been classified into conventional PKCs (α, β, and γ), novel PKCs (δ, ε, η, and θ), and atypical PKCs (ζ and λ/ι). A novel serine-threonine kinase of the protein kinase C (PKC) family has been described and designated as PKCν (PKC nu) which has two putative diacylglycerol binding C1 domains. PKCν is abundantly expressed in human B-cells, and it is a downstream effector for BCR (B-cell antigen receptor)-mediated DAG production. The closest homologues of PKCν are PKD1/PKC+ and PKD2, and together these three kinases form a distinct protein kinase subfamily. They share a predicted tertiary structure that includes two C1 domains contained in their amino-terminal halves, a single central pH domain, and closely homologous kinase domains in their COOH-terminal halves.