Fig. 3. Characterization of AP-1 binding by EMSA. In A, nuclear extracts from bryo 1-differentiated Reh cells were tested for their capacity to recognize the AP-1 consensus sequence. Specific mobility shift and supershift of AP-1-radiolabeled, double-stranded oligonucleotides were used. Complex formation can be seen in Lanes 1 and 3–13. Lane 1, nuclear extract derived from 3T3 SR cells that is used as a positive control. For competition experiments, a 100-fold molar excess of unlabeled, double-stranded, wild-type, or mutant oligonucleotide was included in the DNA binding reaction. Bryo 1 is shown to potentiate AP-1 complex formation in a time-dependent fashion. Polyclonal antibodies against c-Fos, c-Jun, Fos B, Jun B, and Jun D were included in the DNA binding reaction for supershift analysis. B, nuclear lysates taken from Reh cells treated with the MEK-specific inhibitors PD 98059 at a concentration of 20 µM and U0126 at a concentration of 15 µM before bryo 1 showed an inhibition of AP-1/DNA complex formation.