Transcription factor that acts as a key regulator of ciliogenesis (PubMed:22233545). Specifically regulates expression of genes required for cilium assembly and function (PubMed:22233545). Recognizes and binds the X-box, a regulatory motif with DNA sequence 5'-GTNRCC(0-3N)RGYAAC-3' present on promoters (By similarity). Homodimer. Heterodimer; heterodimerizes with other rfx proteins. Mainly expressed in the nucleus and at lower level in cytoplasm. Reduced cilia length in the Kupffer's vesicle and impaired left-right asymmetry. Belongs to the RFX family.