Ubiquilin 4 (UBQLN4)

Sequence comparison revealed that A1U contains an N-terminal ubiquitin-like region, placing it within a large family of similar proteins. In addition, A1U shows substantial homology to human UBQLN2, a protein that binds the ATPase domain of the HSP70-like STCH protein. Expression analyses demonstrated that A1U mRNA is widely expressed as a 4.0-kb transcript and is present in Purkinje cells, the primary site of spinocerebellar ataxia-1 (SCA1) cerebellar pathology.

The A1U protein localized to the nucleus and cytoplasm of transfected COS-1 cells. Sequences important for the transport of A1U into the nucleus appeared to lie within the C terminus. In the nucleus, A1U colocalized with mutant ataxin-1 (ATX1), further demonstrating that A1U interacts with ataxin-1.