Identification of a self-association region within the SCA1 gene product, ataxin-1

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by the expansion of a polyglutamine tract within the SCA1 gene product, ataxin-1. Expansion of this tract is believed to result in a gain of function by the mutant protein, perhaps through altered self-associations or interactions with other cellular proteins. We have used the yeast two hybrid system to determine if ataxin-1 is capable of multimerization. This analysis revealed that ataxin-1 does have the ability to self-associate, however, this association does not appear to be influenced by expansion of the polyglutamine tract. Consistent with this finding, deletion analysis excluded the involvement of the polyglutamine tract in ataxin-1 self-association, and instead localized the multimerization region to amino acids 495-605 of the wild type protein. These results, while identifying an ataxin-1 self-interaction region, fail to support a proposed model of polar-zipper mediated multimerization involving the ataxin-1 polyglutamine tract.