Chromatin-binding factor that repress Notch signaling in the absence of Notch intracellular domain by acting as a CBF1 corepressor. Binds to the HEY promoter and might assist, along with NCOR2, RBPJ-mediated repression. Binds RNA in vitro. May be involved in RNA metabolism (PubMed:21475249). In concert with CIC and ATXN1L, involved in brain development (By similarity). Homooligomer (PubMed:9097953). Interacts with CIC (By similarity). Interacts with ANP32A, PQBP1, UBQLN4, ATXN1L and USP7 (PubMed:9353121, PubMed:11001934, PubMed:12062018, PubMed:12093161, PubMed:16121196). Directly interacts with RBPJ; this interaction is disrupted in the presence of Notch intracellular domain. Competes with ATXN1L for RBPJ-binding (PubMed:21475249). Found in a complex with CIC and ATXN1L (By similarity). Colocalizes with USP7 in the nucleus. At least 2 isoforms are produced. Widely expressed throughout the body. ATXN1 protein levels are directly regulated by PUM1 protein: PUM1 acts by binding to the 3'-UTR of ATXN1 mRNA, affecting ATXN1 mRNA stability and leading to reduced ATXN1 protein levels. The AXH domain is required for interaction with CIC. Ubiquitinated by UBE3A, leading to its degradation by the proteasome. The presence of expanded poly-Gln repeats in spinocerebellar ataxia 1 (SCA1) patients impairs ubiquitination and degradation, leading to accumulation of ATXN1 in neurons and subsequent toxicity. Phosphorylation at Ser-775 increases the pathogenicity of proteins with an expanded polyglutamine tract. Sumoylation is dependent on nuclear localization and phosphorylation at Ser-775. It is reduced in the presence of an expanded polyglutamine tract. The poly-Gln region of ATXN1 is highly polymorphic (4 to 39 repeats) in the normal population and is expanded to about 40-83 repeats in spinocerebellar ataxia 1 (SCA1) patients. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by expansion of the polyglutamine tract to about 40-83 repeats, causing accumulation in neurons and exerting toxicity. Self-association seems to be necessary for formation of nuclear aggregates which are associated with pathogenesis. Belongs to the ATXN1 family. Ataxin-1 entry