Fig. 6. LIN-39 and CEH-20 bind cooperatively to two consensus Hox/PBC binding sites in vitro. The bottom arrow indicates bands corresponding to probes bound to LIN-39 alone and the top arrow indicates bands corresponding to probes bound to LIN-39/CEH-20 heterodimers. In the first four lanes, an oligonucleotide (Antp/Exd) containing a binding site for a Drosophila Hox protein, Antennapedia, and its co-factor, Extradenticle, is used as a positive control. LIN-39 and CEH-20 bind the wild-type site 1 (S1) and site 2 (S2) efficiently, but not the mutated sites (S1M and S2M). Site 2 shows greater binding affinity for LIN-39/CEH-20 heterodimers than does site 1, and LIN-39 alone can bind site 2 but not site 1.