Ubiquitins

Synoviolin (SYVN1) acts as an E3 ubiquitin-protein ligase which accepts ubiquitin specifically from endoplasmic reticulum-associated UBC7 E2 ligase and transfers it to substrates subsequently promoting their degradation. For instance, SYVN1 protects neurons from apoptosis induced by polyglutamine-expanded huntingtin (HTT) or unfolded GPR37 by promoting their degradation. SYVN1 is up-regulated in synovial tissues from patients with rheumatoid arthritis.

F-box/WD repeat-containing protein 8 (FBXW8) is a substrate-recognition component of a SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin-protein ligase complex, which mediates the ubiquitination and subsequent proteosomal degradation of target proteins. FBXW8 is a member of the F-box protein family, members of which are characterized by an approximately 40 amino acid motif, the F-box.

Transcription intermediary factor 1-beta (TIF1-beta) forms a complex with a KRAB-domain transcription factor and increases the efficiency of KRAB-mediated repression. TIF1-beta silences transcription through an interaction with HP1 proteins. TIF1-beta acts as a corepressor of transcription for the KRAB zinc finger proteins and as a moderator of the repression activity. TIF1-beta plays a role as a coactivator for CEBPB and NR3C1 in the transcriptional activation of the Alpha-1-acid glycoprotein gene.

Autoimmune regulator (APECED) is a transcriptional regulator that binds to DNA as a dimer or as a tetramer, but not as a monomer. APECED binds to G-doublets in an A/T-rich environment; the preferred motif is a tandem repeat of 5'-. ATTGGTTA-3' combined with a 5'-TTATTA-3' box. APECED binds to chromatin and interacts selectively with histone H3 that is not methylated at 'Lys-4', not phosphorylated at 'Thr-3' and not methylated at 'Arg-2'. APECED functions as a sensor of histone H3 modifications that are important for the epigenetic regulation of gene expression.

E3 SUMO-protein ligase CBX4 (CBX4) is a protein ligase which facilitates SUMO1 conjugation by UBE2I. CBX4 is a component of the Polycomb group (PcG) multiprotein PRC1 complex, a complex required to maintain the transcriptionally repressive state of many genes, including Hox genes, throughout development. The PcG PRC1 complex acts via chromatin remodeling and modification of histones; and it mediates monoubiquitination of histone H2A 'Lys-119', rendering chromatin heritably changed in its expressibility.