Fig. 1.

Screening the Prestwick chemical library. (A) Selection assay for CAG repeat contractions. Large CAG repeat tracts are spliced aberrantly, preventing expression of functional HRPT and making the cells HAT sensitive (HAT^S). When the repeat tract is 38 units or fewer, sufficient correctly spliced message is produced to permit expression of enough HPRT to become HAT resistant (HAT^R). (B) Design of chemical screen. FLAH25 cells were plated at near confluence in 96-well plates, treated for 3 days with chemicals in the presence of doxycycline, and then replated for HAT selection in six-well plates.