RING finger, HC subclass, found in transcription inknown asiary factor 1-beta (TIF1-beta)
TIF1-beta, also known as Kruppel-associated Box (KRAB)-associated protein 1 (KAP-1), KRAB-interacting protein 1 (KRIP-1), nuclear co-repressor KAP-1, RING finger protein 96, tripartite motif-containing protein 28 (TRIM28), or E3 SUMO-protein ligase TRIM28, belongs to the C-VI subclass of TRIM (tripartite motif) family of proteins that are defined by their N-terminal RBCC (RING, Bbox, and coiled coil) domains, including three consecutive zinc-binding domains, a C3HC4-type RING-HC finger, Bbox1 and Bbox2, and a coiled coil region, as well as a plant homeodomain (PHD), and a bromodomain (Bromo) positioned C-terminal to the RBCC domain. It acts as a nuclear co-repressor that plays a role in transcription and in the DNA damage response. Upon DNA damage, the phosphorylation of KAP-1 on serine 824 by the ataxia telangiectasia-mutated (ATM) kinase enhances cell survival and facilitates chromatin relaxation and heterochromatic DNA repair. It also regulates CHD3 nucleosome remodeling during the DNA double-strand break (DSB) response. Meanwhile, KAP-1 can be dephosphorylated by protein phosphatase PP4C in the DNA damage response. Moreover, KAP-1 is a co-activator of the orphan nuclear receptor NGFI-B (or Nur77) and is involved in NGFI-B-dependent transcription. It is also a coiled-coil binding partner, substrate and activator of the c-Fes protein tyrosine kinase. The N-terminal RBCC domains of TIF1-beta are responsible for the interaction with KRAB zinc finger proteins (KRAB-ZFPs), MDM2, MM1, C/EBPbeta, and the regulation of homo- and heterodimerization. The C-terminal PHD/Bromo domains are involved in interacting with SETDB1, Mi-2alpha and other proteins to form complexes with histone deacetylase or methyltransferase activity.