The transcriptional intermediary factor 1 (TIF1) family represents a group of proteins with multiple histone-binding domains. In humans, this family comprises four proteins, TIF1alpha/TRIM24, TIF1beta/TRIM28/KAP1, TIF1gamma/TRIM33/Ectodermin, and TIF1delta/TRIM66, which are characterized by an amino-terminal tripartite motif (TRIM) domain consisting of a RING domain, two B boxes, a coiled-coil domain, and a carboxy-terminal PHD finger and bromodomain . Despite their similar overall structure, these proteins have diverse roles in transcriptional regulation. TIF1alpha functions as a ligand-dependent nuclear receptor coregulator and more recently has been implicated in regulating p53 stability . TIF1beta is an intrinsic component of the N-CoR1 corepressor complex and the NuRD nucleosome-remodeling complex and functions as a corepressor for Kruppel-associated box (KRAB) zinc-finger transcription factors. Furthermore, TIF1beta promotes heterochromatin-mediated gene silencing formation by serving as a cofactor for heterochromatin protein HP1 . TIF1delta expression is restricted to the testis and has been shown to interact with HP1gamma .
