the disease (9). Colomer et al used a yeast two-hybrid system to isolate rat cDNA encoding part of a protein that interacts with HAP1. Northern blot electrophoresis indicated the brain-specific location of this protein (2). The protein contains a guanine nucleotide exchange factor domain that is likely to be rac-1 specific, a pleckstrin homology domain, and spectrin-like repeat units. These data support the hypothesis that Huntington is involved in vesi