Figure 4. DNA binding activity of Vsx1 and 2 and transcriptional transactivation activity of Vsx2 isoforms. A: Vsx1 and Vsx2 can bind the photoreceptor conserved element-1 (PCE-1) site in vitro. Electrophoretic mobility shift assay (EMSA) performed using a radiolabeled PCE-1 probe, in vitro translated Vsx1 or Vsx2 proteins, and unlabeled wild-type (W) or mutant (M) PCE-1, BAT (B), or Ret4 (R) oligonucleotide competitors. Arrows indicate specific DNA–protein complexes. B: Vsx2_L, but not Vsx2_S, inhibits activation of XOP-Luc by otx5b and XLmaf. The luciferase assay was performed using lysates from embryos coinjected with the XOP-Luc reporter plasmid and otx5b + XLmaf and/or Vsx2_L or Vsx2_S RNAs as shown. Values are presented as fold mean normalized luciferase activity (relative to the reporter only, no effector control); error bars denote standard deviation from the mean. P, protein; C, competitor. * p<0.03; ** p<0.01.