Figure 4.

HY5 Interferes with FHY3 for Binding to the FHY1 Promoter.

(A) GST-FHY3N, GST-HY5, and GST-HY5C proteins, but not GST by itself, bind to the wild-type (WT) FHY1 promoter but not to the FBS (GST-FHY3N) and ACE (GST-HY5 and GST-HY5C) mutant (mut) probes. The sequences of FHY1p-ACE1 wild-type and mutant probes are shown in Figure 2A. The sequence of FHY1p-FBS mut probe is identical to that of the FHY1p-ACE1 wild-type probe except that the FBS motif (CACGCGC) was mutated to CAttttC. FP, free probe.

(B) Increasing amounts of GST-HY5C protein (lanes 7 to 9), but not GST (lanes 4 to 6), decrease the binding of GST-FHY3N to the wild-type FHY1 promoter. Interaction between HY5C and FHY3N prevents GST-FHY3N from binding to the promoter (lanes 10 to 12). The triangles in lanes 3 and 9 indicate a polymer of HY5C bound to the probe.