The IDR regulates SUFU activity. (a) SUFU-FL (FL), SUFU-Δ (Δ) and SUFU-SH (SH) all bind GLI1 when co-expressed in Cos-7 cells, as shown by Co-IP. (b, c) SUFU-FL and SUFU-Δ repress GLI1-induced reporter gene activity in HEK 293 cells (b) and suppress constitutive pathway activity in Sufu−/− cells (c) with similar efficiency. (d) SUFU-Δ, SUFU-SH and SUFU-IDRfly (IDRfly) expressed in Sufu−/− cells are unable to mediate Hh pathway reactivation induced by the SMO agonist SAG. Error bars indicate the range of data in three parallel samples. (e) Schematic model of the regulatory role of SUFU with and without an intact IDR. Green and red colours indicate activated and repressed states of proteins, respectively.