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 (By similarity). Heterotrimer of KIFAP3, KIF3A and KIF3B. Interacts with RAP1GDS1/SMG GDS. Interacts with SMC3 subunit of the cohesin complex. Phosphorylated on tyrosine residues by SRC in vitro; this reduces the binding affinity of the protein for RAP1GDS1.