Fig. 4. Binding of a Hox-Pbx-Prep ternary complex requires intact PH and P/M sites. (A,B) In vitro synthesized proteins were subjected to EMSA with different radiolabeled probes (drawn below the gels) containing the PH and/or P/M sites. (A) Pbx-Prep (arrow in lanes 4,5), but not Pbx-Hox, heterodimers are formed on the 30 bp probe. (B) A retarded band (arrow in lane 5) forms only in the presence of Hoxb1, Pbx1a and Prep1 proteins on a 233 bp probe containing PH and P/M sites in their native context (left panel), but not on a probe carrying a PH site deletion (middle panel) or a P/M site mutation (same as that in Fig. 3J) (right panel). The ternary complex is selectively inhibited by adding specific antibodies (lanes 6-8). Asterisks indicate unspecific bindings. RRL, unprogrammed rabbit reticulocyte lysate; FP, free probe.