Involved in tethering the chromosomes to the spindle pole and in chromosome movement. Binds to the tail domain of the KIF3A/KIF3B heterodimer to form a heterotrimeric KIF3 complex and may regulate the membrane binding of this complex. Interacts with SMC3 subunit of the cohesin complex (By similarity). Heterotrimer of KIFAP3, KIF3A and KIF3B. Interacts with RAP1GDS1/SMG GDS. Phosphorylated on tyrosine residues by SRC in vitro; this reduces the binding affinity of the protein for RAP1GDS1.