COMPLEX-FORMATION OF SMAP KAP3, A KIF3A/B ATPASE MOTOR-ASSOCIATED PROTEIN, WITH A HUMAN CHROMOSOME-ASSOCIATED POLYPEPTIDE/

We have recently isolated SMAP (Smg GDS-associated protein; Smg GDS: s mall G protein GDP dissociation stimulator) as a novel Smg GDS-associa ted protein, which has Armadillo repeats and is phosphorylated by Src tyrosine kinase. SMAP is a human counterpart of mouse KAP3 (kinesin su perfamily-associated protein) that is associated with mouse KIF3A/B (a kinesin superfamily protein), which functions as a microtubule-based ATPase motor for organelle transport, We isolated here a SMAP-interact ing protein from a human brain cDNA library, identified it to be a hum an homolog of Xenopus XCAP-E (Xenopus chromosome-associated polypeptid e), a subunit of condensins that regulate the assembly and structural maintenance of mitotic chromosomes, and named it HCAP (Human chromosom e-associated polypeptide), Tissue and subcellular distribution analyse s indicated that HCAP was ubiquitously expressed and highly concentrat ed in the nuclear fraction, where SMAP and KIF3B were also present, SM AP was extracted as a ternary complex with HCAP and KIF3B from the nuc lear fraction in the presence of Mg-ATP. The results suggest that SMAP /KAP3 serves as a linker between HCAP and KIF3A/B in the nucleus, and that SMAP/KAP3 plays a role in the interaction of chromosomes with an ATPase motor protein.