The cc2d1a gene family consists of two homologues, CC2D1A (Freud-1) and CC2D1B (Freud-2). Freud-1 is a calcium-regulated repressor of serotonine receptor 5-HT1A and dopamine-D2 receptor expression [, ]. Mutations in cc2d1a has been linked to nonsyndromic mental retardation [, ].CC2D1A/freud-1 and CC2D1B/freud-2 share conserved domains, including several DM14 domains that are specific to this protein family, a C-terminal helix-loop-helix domain, and a C2 domain. The Freud-1 C2 domain is thought to be calcium insensitive and it lacks several acidic residues that mediate calcium binding of the PKC C2 domain. In addition, it contains a poly-basic insert that is not present in calcium-dependent C2 domains and may function as a nuclear localization signal []. The Freud-1 C2 domain appears to be essential for its DNA binding and repressor function; it may mediate protein-protein interactions [].