ReviewThe Molecular Motor Toolbox for Intracellular Transport

transport involves molecular motor proteins that carry cargo directionally along a cytoskeletal track (myosins along actin and kinesins and dyneins along microtu-the origins of the molecular motors and the intracellular transport strategies employed by various organisms. While prokaryotes contain cytoskeletal filaments, the Eukaryotic cells create internal order by using protein motors to transport molecules and organelles along cytoskeletal motors appear to be an early eukaryotic invention. Several types of cargo-transporting molecular cytoskeletal tracks. Recent genomic and functional studies suggest that five cargo-carrying motors motors emerged in unicellular eukaryotes, and this same ancient " Toolbox " of motors expanded to meet the ma-emerged in primitive eukaryotes and have been widely used throughout evolution. The complexity of these jority of transport needs of multicellular organisms. These cargo-transporting motors will be the focus of this " Toolbox " motors expanded in higher eukaryotes through gene duplication, alternative splicing, and the review. Molecular motors also are used for organizing cytoskeletal filaments (e.g., controlling their dynamics, addition of associated subunits, which enabled new cargoes to be transported. Remarkably, fungi, para-collecting them into bundles, and causing filament-filament sliding). Intracellular transport also can be driven sites, plants, and animals have distinct subsets of Toolbox motors in their genomes, suggesting an by attaching cargo to the ends of polymerizing or depo-lymerizing microtubule or actin filaments. However, underlying diversity of strategies for intracellular transport. these aspects of motor function and cytoskeletal dynamics will not be discussed here. A cell, like a metropolitan city, must organize its bustling community of macromolecules. Setting meeting points Prokaryotes Contain Cytoskeletal Filaments and establishing the timing of transactions are of funda-Related to Actin and Tubulin mental importance for cell behavior. The high degree of Although simpler in overall design than eukaryotes, pro-spatial/temporal organization of molecules and organ-karyotes also must physically separate replicated DNA elles within cells is made possible by protein machines and establish a central division plane, and some bacteria that transport components to various destinations have well-defined asymmetric cell shapes. Recently, within the cytoplasm. several of the proteins involved in these processes were Landmark discoveries of cytoplasmic transport have discovered to be antecedents of eukaryotic actin and been, and continue to be, made through advances in microtubules (van den Ent et al., 2001a). FtsZ, which microscopy. Intracellular motion was first observed in forms filaments that encircle the middle of the bacterium the alga Chara by Bonaventura Corti in the late 18 th …