PKC theta localizes at the interface between T cells and antigen presenting cells. Upon the T cell activation and release of the second messengers Ca++ and DAG by PLC-gamma1, DAG binds to the C1 domain of the PKC theta thereby enhances the attachment to the plasma membrane. Upon membrane translocation, PKC theta is phosphorylated at tyrosine 90 in the C2 like domain. This phosphorylation is mediated by the tyrosine kinase Lck. These association and, most likely, other regulatory interactions, lead to a change in PKC theta conformation into an open, active state whereby it can now access its substrates and phosphorylate them.