FIZ1 alters the CRX-mediated activation of two Opsin promoters. Two CRX-activated proximal promoters were used from the photoreceptor genes: M-Opsin and S-Opsin. Firefly luciferase activity was normalized to Renilla-luciferase activity (pRL-CMV). Fold Activation is relative to empty expression vectors. A) the M-Opsin promoter luciferase-reporter construct, Mop250-Luc, or B) the S-Opsin promoter luciferase-reporter construct, Sop552-Luc. Triplicate wells of CV1 cells were co-transfected with expression vectors for CRX, FIZ1, and NRL in the combinations indicated. CRX could activate both test promoters, relative to empty vectors. NRL or FIZ1 alone had no activation effect on either promoter. NRL combined with CRX did not alter the activation potential from that of CRX alone. FIZ1 combined with CRX significantly altered the CRX-mediated activation of both test promoters, when compared to CRX alone. Bars represent ± SD (n = 3). Statistical comparisons are described in results.