A CLASS-VI UNCONVENTIONAL MYOSIN IS ASSOCIATED WITH A HOMOLOG OF A MICROTUBULE-BINDING PROTEIN, CYTOPLASMIC LINKER PROTEIN-170, IN NEURONS AND AT THE POSTERIOR POLE OF DROSOPHILA EMBRYOS

Coordination of cellular organization requires the interaction of the cytoskeletal filament systems. Recently, several lines of investigatio n have suggested that transport of cellular components along both micr otubules and actin filaments is important for cellular organization an d function. We report here on molecules that may mediate coordination between the actin and microtubule cytoskeletons. We have identified a 195-kD protein that coimmunoprecipitates with a class VI. myosin, Dros ophila 95F unconventional myosin. Cloning and sequencing of the gene e ncoding the 195-kD protein reveals that it is the first homologue iden tified of cytoplasmic linker protein (CLIP)-170, a protein that links endocytic vesicles to microtubules. We have named this protein D-CLIP- 190 (the predicted molecular mass is 189 kD) based on its similarity t o CLIP-170 and its ability to cosediment with microtubules. The simila rity between D-CLIP-190 and CLIP-170 extends throughout the length of the proteins, and they have a number of predicted sequence and structu ral features in common. 95F myosin and D-CLIP-190 are coexpressed in a number of tissues during embryogenesis in Drosophila. In the axonal p rocesses of neurons, they are colocalized in the same particulate stru ctures, which resemble vesicles. They are also colocalized at the post erior pole of the early embryo, and this localization is dependent on the actin cytoskeleton. The association of a myosin and a homologue of a microtubule-binding protein in the nervous system and at the poster ior pole, where both microtubule and actin-dependent processes are kno wn to be important, leads us to speculate that these two proteins may functionally link the actin and microtubule cytoskeletons.