Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a polyglutam
ine tract in ataxin-2, a protein of unknown function. Using the yeast two-h
ybrid system, we identified a novel protein, A2BP1 (ataxin-2 binding protei
n 1) which binds to the C-terminus of ataxin-2. Northern blot analysis show
ed that A2BP1 was predominantly expressed in muscle and brain. By immunocfl
uorescent staining, A2BP1 and ataxin-2 were both localized to the trans-Gol
gi network. Immunocytochemistry showed that A2BP1 was expressed in the cyto
plasm of Purkinje cells and dentate neurons in a pattern similar to that se
en for ataxin-2 labeling. Western blot analysis of subcellular fractions in
dicated enrichment of A2BP1 in the same fractions as ataxin-2, Sequence ana
lysis of the A2BP1 cDNA revealed an RNP motif that is highly conserved amon
g RNA-binding proteins. A2BP1 had striking homology with a human cDNA clone
, P83A20, of unknown function and at least two copies of A2BP1 homologs are
found in the Caenorhabditis elegans genome database. A2BP1 and related pro
teins appear to form a novel gene family sharing RNA-binding motifs.