Pii: S0962-8924(99)01665-7

M38 T here are many different types of molecular motor; some of them move linearly along polymers, whereas others undergo rotary motions (Table 1). Many other nucleotidases, including tubulin, actin, chaperones and some G proteins, should perhaps be considered as molecular motors as well because the generation of mechanical strain is central to their activity. However, the primary focus of this review is on linear cytoskeletal motors. For detailed information on the structure, mechanism, superfamily composition and biological roles of molecular motors, the reader is referred to recent collections of reviews on these subjects (Box 1).