protein kinase C conserved region 1 (C1 domain) found in the atypical protein kinase C (aPKC) familyPKCs are classified into three groups (classical, atypical, and novel) depending on their mode of activation and the structural characteristics of their regulatory domain. aPKCs only require phosphatidylserine (PS) for activation. They contain a C2-like region, instead of a calcium-binding (C2) region found in classical PKCs, in their regulatory domain. There are two aPKC isoforms, zeta and iota. aPKCs are involved in many cellular functions including proliferation, migration, apoptosis, polarity maintenance and cytoskeletal regulation. They also play a critical role in the regulation of glucose metabolism and in the pathogenesis of type 2 diabetes. PKC-zeta plays a critical role in activating the glucose transport response. It is activated by glucose, insulin, and exercise through diverse pathways. PKC-zeta also plays a central role in maintaining cell polarity in yeast and mammalian cells. In addition, it affects actin remodeling in muscle cells. PKC-iota is directly implicated in carcinogenesis. It is critical to oncogenic signaling mediated by Ras and Bcr-Abl. The PKC-iota gene is the target of tumor-specific gene amplification in many human cancers, and has been identified as a human oncogene. In addition to its role in transformed growth, PKC-iota also promotes invasion, chemoresistance, and tumor cell survival. Expression profiling of PKC-iota is a prognostic marker of poor clinical outcome in several human cancers. PKC-iota also plays a role in establishing cell polarity, and has critical embryonic functions. Members of this family contain one C1 domain. The C1 domain is a cysteine-rich zinc binding domain that does not bind DNA nor possess structural similarity to conventional zinc finger domains; it contains two separate Zn(2+)-binding sites.