Component of the axonemal radial spoke head which plays an important role in ciliary motility (PubMed:19200523). Essential for triplet radial spokes (RS1, RS2 and RS3) head assembly in the motile cilia (By similarity). Interacts with RSPH6A. Radial spoke. Expressed in trachea, lungs, and testes (PubMed:23993197). Very strong expression is detected in nasal brushings (PubMed:19200523). The disease is caused by variants affecting the gene represented in this entry. Belongs to the flagellar radial spoke RSP4/6 family.