HIP-I: a huntingtin interacting protein isolated by the yeast two- hybrid system

We report the discovery of the huntingtin interacting protein I (HIP-I)which binds specifically to the N-terminus of human huntingtin, both in thetwo-hybrid screen and in in vitro binding experiments. For the interactionin vivo, a protein region downstream of the polyglutamine stretch inhuntingtin is essential. The HIP1 cDNA isolated by the two- hybrid screenencodes a 55 kDa fragment of a novel protein. Using an affinity-purifiedpolyclonal antibody raised against recombinant HIP-I, a protein of 116 kDawas detected in brain extracts by Western blot analysis. The predictedamino acid sequence of the HIP-I fragment exhibits significant similarityto cytoskeleton proteins, suggesting that HIP-I and huntingtin play afunctional role in the cell filament networks. The HIP1 gene isubiquitously expressed in different brain regions at low level. HIP-I isenriched in human brain but can also be detected in other human tissues aswell as in mouse brain. HIP-I and huntingtin behave almost identicallyduring subcellular fractionation and both proteins are enriched in themembrane containing fractions.