UL97 prevents aggregation of ataxin-3 containing expanded polyQ track. HeLa cells were cotransfected with AT3-72Q-myc and either a vector lacking UL97 (A), a vector encoding UL97-V5 (B), or a vector encoding UL97/K355M–V5 (C). After 72 h, cells were processed for IF with anti-myc antibodies to detect AT3-72Q and anti-V5 antibodies to detect UL97. Cells expressing AT3-72Q were scored for aggregates in three independent experiments, and the graph represents the percentage of cells containing aggregates (D). AT3-72Q-myc forms large cytoplasmic and nuclear aggregates in control cells and in cells expressing the catalytically inactive UL97/K355M. Aggregates are not detected or greatly reduced in cells that express UL97. The difference is significant (p<0.0007). Bars, 19 µm.