FIG. 4.

The truncated Mod(mdg4)-67.2^u1 and Mod(mdg4)^T6 proteins do not interact with Su(Hw). The Mod(mdg4)-67.2 protein contains a BTB/POZ motif (gray box) at the N terminus common to most if not all Mod(mdg4) proteins, a glutamine-rich (Q-rich) region, and a unique C terminus (cross-hatched box) (3). ³⁵S-labeled fragments of Mod(mdg4)-67.2, including fragments that mimic the predicted mutant proteins produced by the mod(mdg4)^u1 and mod(mdg4)^T6 alleles, were prepared by translation in vitro and tested for their ability to bind GST-Su(Hw)-CTD beads and GST-only control beads. The autoradiograms of SDS-PAGE gels show the amount of input labeled protein (load, lane 1) and the amount that bound to the beads indicated at the tops of lanes 2 and 3. The full-length Mod(mdg4)-67.2 and the C-terminal fragment of Mod(mdg4)-7.2 both bound to the GST-Su(Hw)-CTD beads (lane 3), while the truncated Mod(mdg4)-67.2^u1, Mod(mdg4)-67.2^T6, and N-terminal fragment of Mod(mdg4)-67.2 did not (lane 3). As expected, the luciferase (luc) control protein also did not bind to any of the beads. In the lowest panel, nearly equal amounts of labeled full-length Mod(mdg4)-67.2 and Mod(mdg4)-67.2^u1 were prepared by cotranslation in vitro. In this case, a small but significant amount of Mod(mdg4)-67.2^u1 was retained (lane 6, arrow). All the results shown were reproducible in independent experiments.