An isoform of kinesin light chain specific for the Golgi complex

Conventional kinesin is a motor protein implicated in the transport of a variety of cytoplasmic organelles along microtubules. The kinesin molecule consists of two heavy chains with motor domains at their amino termini and two light chains, which, together with the carboxyl termini of the heavy chains, are proposed to mediate binding to cargoes. Since the light chains are represented by multiple isoforms diverging at their carboxyl termini they are presumed to specify kinesin targeting to organelles. Previously, we isolated five cDNAs, encoding hamster kinesin light chain isoforms, and found that one of them (B or C) preferentially associated with mitochondria. To obtain additional evidence proving the specific location of various kinesin light chain isoforms on organelles, we made an antibody against a 56 amino-acid sequence found at the carboxyl-terminal regions of the hamster D and E isoforms. By indirect immunofluorescence, this antibody specifically labeled the Golgi complex in cultured cells. In western blots of total cell homogenates, it recognized two close polypeptides, one of which co-purified with the Golgi membranes. Thus, the results of this and previous studies demonstrate that different kinesin light chains are associated with different organelles in cells.