Protein kinase C-like, phorbol ester/diacylglycerol binding <p>Diacylglycerol (DAG) is an important second messenger. Phorbol esters (PE) are analogues of DAG and potent tumour promoters that cause a variety of physiological changes when administered to both cells and tissues. DAG activates a family of serine/threonine protein kinases, collectively known as protein kinase C (PKC) [<cite idref="PUB00001427"/>]. Phorbol esters can directly stimulate PKC. The N-terminal region of PKC, known as C1, has been shown [<cite idref="PUB00004685"/>] to bind PE and DAG in a phospholipid and zinc-dependent fashion. The C1 region contains one or two copies (depending on the isozyme of PKC) of a cysteine-rich domain, which is about 50 amino-acid residues long, and which is essential for DAG/PE-binding. The DAG/PE-binding domain binds two zinc ions; the ligands of these metal ions are probably the six cysteines and two histidines that are conserved in this domain.</p>