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 (PubMed:21475249). Can suppress ATXN1 cytotoxicity in spinocerebellar ataxia type 1 (SCA1). In concert with CIC and ATXN1, involved in brain development (By similarity). Homodimer. Interacts with CIC (By similarity). Interacts (via AXH domain) with NCOR2. Interacts with ATXN1 (PubMed:16121196). Directly interacts with RBPJ; this interaction is disrupted in the presence of Notch intracellular domain. Competes with ATXN1 for RBPJ-binding (PubMed:21475249). Found in a complex with CIC and ATXN1 (By similarity). Forms nuclear foci. Colocalizes with NCOR2 and HDAC3. Distributed beyond the nucleus into the cell body and dendrites in Purkinje cells and in inferior olive cells. Expressed in cerebellum and cerebral cortex. Belongs to the ATXN1 family.