Full length 3xFlag7Q-htt and HA7Q-htt do not co-immunoprecipitate. 0.5 mg cytoplasmic extract prepared from the cerebellum (Cb) and striatum (Str) of a 1 month-old Hdh 3xFlag7Q/HA7Q mouse (A) and from the forebrain of a 12 month-old Hdh3xFlag7Q/HA7Q mouse (B) was immunoprecipitated with anti-FLAG M2 agarose beads. The antibody non-bound sample (NB) represents 10% of the total NB fraction, and the antibody-bound sample (B) represents 33% of the total B sample. Protein was resolved on 5% SDS-PAGE, transferred to PVDF membranes, and probed with either FLAG M2 or HA.11 antibodies. In both the 1month- and 12 month-old mice, HA7Q-htt was found entirely in the NB fraction suggesting that there is no stable interaction between full-length soluble 7Q-htt. The positions of htt, and a 250 kD protein size standard are indicated.