Component of the BBSome complex (By similarity). The BBSome complex is thought to function as a coat complex required for sorting of specific membrane proteins to the primary cilia (By similarity). The BBSome complex is required for ciliogenesis but is dispensable for centriolar satellite function (By similarity). Required for proper BBSome complex assembly and its ciliary localization (By similarity). May be required for microtubule anchoring at the centrosome but not for microtubule nucleation (By similarity). May be required for the dynein-mediated transport of pericentriolar proteins to the centrosome (By similarity). Required, redundantly with bbs-5, for cilia biogenesis and both the assembly and movement of intraflagellar transport proteins along the ciliary axoneme (PubMed:22922713, PubMed:26150102). Plays a role in the removal of degraded mechanosensory receptors within the cilia (PubMed:26150102). Part of BBSome complex, that contains at least bbs-1, bbs-2, bbs-4, bbs-5, osm-12, bbs-8/ttc-8 and bbs-9 (By similarity). Interacts (via C-terminus) with bbs-5; the interaction is direct (PubMed:26150102). Single mutants do not display any obvious defects in ciliogenesis. Double bbs-4 and bbs-5 mutants display a defect in cilia structure and function. This is characterized by an increased accumulation and mislocalization of intraflagellar transport proteins and impaired movement of intraflagellar transport proteins along the ciliary axoneme. Double mutants also have defective polycystin-mediated cilia signaling and mislocalized and increased accumulation of mechanosensory receptors pkd-2, osm-9 and odr-10 within cilia. Belongs to the BBS4 family.