Transcription factor that acts as a key regulator of ciliogenesis. Specifically regulates expression of genes required for cilium assembly and function. Recognizes and binds the X-box, a regulatory motif with DNA sequence 5'-GTNRCC(0-3N)RGYAAC-3' present on promoters. Required for neural tube closure and neural ciliogenesis. Homodimer. Heterodimer; heterodimerizes with other rfx proteins. Mainly expressed in the nucleus and at lower level in cytoplasm. Belongs to the RFX family.