Figure 7.

Model for Tcf, long Grg and Grg-5 functions. Expression of Tcf target genes is activated when Tcf is associated with β-catenin and repressed when Tcf binds Groucho. Here we show that the function of Grg-5 provides another level of regulation. When in a complex, both the long repressor Grg and Grg-5 are bound to Tcf, a less competent repressor is formed, since less HDAC activity is tethered to the promotor. When Grg-5 replaces the longer repressor entirely from the complex with Tcf, repression is absent because HDAC activity is lacking.