This family of proteins is found in eukaryotes. Proteins in this family are typically between 49 and 781 amino acids in length. There is a conserved IQT sequence motif. ATXN1 directly binds Capicua and modulates Capicua repressor activity in Drosophila and mammalian cells. The polyglutamine expanded mutant type of ATXN-1 does not bind Capicua with as high affinity as wild-type ATXN-1. It is associated with spinocerebellar ataxia type 1 (SCA1).