A SPECIFIC LIGHT-CHAIN OF KINESIN ASSOCIATES WITH MITOCHONDRIA IN CULTURED-CELLS

The motor protein kinesin is implicated in the intracellular transport of organelles along microtubules. Kinesin light chains (KLCs) have be en suggested to mediate the selective binding of kinesin to its cargo. To test this hypothesis, we isolated KLC cDNA clones from a CHO-KI ex pression library. Using sequence analysis, they were found to encode f ive distinct isoforms of KLCs. The primary region of variability Lies at the carboxyl termini, which were identical or highly homologous to carboxyl-terminal regions of rat KLC B and C, human KLCs, sea urchin K LC isoforms 1-3, and squid KLCs. To examine whether the KLC isoforms a ssociate with different cytoplasmic organelles, we made an antibody sp ecific for a 10-amino acid sequence unique to B and C isoforms. In an indirect immunofluorescence assay, this antibody specifically labeled mitochondria in cultured CV-1 cells and human skin fibroblasts. On Wes tern blots of total cell homogenates, it recognized a single KLC isofo rm, which copurified with mitochondria. Taken together, these data ind icate a specific association of a particular KLC (B type) with mitocho ndria, revealing that different KLC isoforms can target kinesin to dif ferent cargoes.