PHD finger found in the transcriptional intermediary factor 1 (TIF1) family and similar proteins
The TIF1 family of transcriptional cofactors includes TIF1alpha (TRIM24), TIF1beta (TRIM28), TIF1gamma (TRIM33), and TIF1delta (TRIM66), which are characterized by an N-terminal RING-finger B-box coiled-coil (RBCC/TRIM) motif and plant homeodomain (PHD) finger followed by a bromodomain in the C-terminal region. TIF1 proteins couple chromatin modifications to transcriptional regulation, signaling, and tumor suppression. They exert a deacetylase-dependent silencing effect when tethered to a promoter region. TIF1alpha, TIF1beta, and TIF1delta can homodimerize and contain a PXVXL motif necessary and sufficient for heterochromatin protein 1(HP1) binding. TIF1alpha and TIF1beta bind nuclear receptors and Kruppel-associated boxes (KRAB) specifically and respectively. In contrast, TIF1delta appears to lack nuclear receptor- and KRAB-binding activity. Moreover, TIF1delta is specifically involved in heterochromatin-mediated gene silencing during postmeiotic phases of spermatogenesis. TIF1gamma is structurally closely related to TIF1alpha and TIF1beta, but has very little functional features in common with them. It does not interact with the KRAB silencing domain of KOX1 or the heterochromatinic proteins HP1alpha, beta, and gamma. It cannot bind to nuclear receptors (NRs). This family also includes Sp100/Sp140 family proteins, the nuclear body SP100 and SP140. Sp110 is a leukocyte-specific component of the nuclear body. It may function as a nuclear hormone receptor transcriptional coactivator that may play a role in inducing differentiation of myeloid cells. It is also involved in resisting intracellular pathogens and functions as an important drug target for preventing intracellular pathogen diseases, such as tuberculosis, hepatic veno-occlusive disease, and intracellular cancers. SP140 is an interferon inducible nuclear leukocyte-specific protein involved in primary biliary cirrhosis and a risk factor in chronic lymphocytic leukemia. It is also implicated in innate immune response to human immunodeficiency virus type 1 (HIV-1) by binding to the virus viral infectivity factor (Vif) protein. Both Sp110 and Sp140 contain a SAND domain, a plant homeodomain (PHD) finger, and a bromodomain (BRD).