Microtubule-based molecular motor that transport intracellular cargos, such as vesicles, organelles and protein complexes. Uses ATP hydrolysis to generate force to bind and move along the microtubule (By similarity). Plays a role in cilia formation. Required for photoreceptor development (PubMed:22308397, PubMed:28855254). Heterodimer of KIF3A and KIF3B. KIF3A/KIF3B heterodimer interacts with KIFAP3 forming a heterotrimeric (KIF3A/KIF3B/KIFAP3) complex. Loss of function of Kif3b only results in ciliogenesis defects in a subset of cilia. Robust cilia are still present in the central nervous system. Mutant have rapid rod degeneration and delayed outer segment genesis, but cones appear normal. The mild phenotype of kif3b mutants may be related to the presence of the kif3c protein. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family.