Enables protein kinase binding activity. Involved in negative regulation of smoothened signaling pathway and regulation of DNA-templated transcription. Acts upstream of or within negative regulation of transcription by RNA polymerase II. Located in cytoplasm and nucleoplasm. Part of GLI-SUFU complex. Implicated in Joubert syndrome 32; familial meningioma; medulloblastoma; and nevoid basal cell carcinoma syndrome 2. Biomarker of brain glioblastoma multiforme.