UBQLN4
Description
The UBQLN4 (ubiquilin 4) is a protein-coding gene located on chromosome 1.
Ubiquilin 4 is a protein in humans that is encoded by the UBQLN4 gene. Ubiquilin 4 regulates proteasomal protein degradation.
== Similarity to Other Proteins == Human UBQLN4 shares a high degree of similarity with related ubiquilins including UBQLN1 and UBQLN2.
UBQLN4, also known as Ataxin-1 interacting ubiquitin-like protein (A1U), is a regulator of protein degradation that targets misfolded, mislocalized, or accumulated proteins for proteasomal degradation. It acts by binding polyubiquitin chains via its UBA domain and interacting with proteasome subunits via its ubiquitin-like domain. UBQLN4 also plays a key role in DNA repair by repressing homologous recombination repair. In response to DNA damage, it is recruited to damaged chromatin and removes ubiquitinated MRE11, leading to its degradation by the proteasome. This prevents homologous recombination repair and redirects DNA repair toward non-homologous end joining (NHEJ). UBQLN4 specifically binds mislocalized transmembrane-containing proteins and targets them for degradation. It collaborates with DESI1/POST in exporting ubiquitinated proteins from the nucleus to the cytoplasm. UBQLN4 also regulates the degradation of non-ubiquitinated GJA1. As an adapter protein, it recruits UBQLN1 to the autophagy machinery, mediates its association with autophagosomes and LC3 (MAP1LC3A/B/C), and potentially assists in autophagosome maturation by promoting fusion with lysosomes.
UBQLN4 is also known as A1U, A1Up, C1orf6, CIP75, UBIN.
