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Cover  This month's cover shows a gallery of electronmicrographic images of axoplasmic organelles labeled by immunogold for nonmuscle myosin II. Organelles in the giant axon of the squid were shown to move on invisible tracks, sensitive to cytochalasin and thus presumed to be actin filaments in 1992 (Kuznetsov, S.A., Langford, G.M., and Weiss, D.G. Actin-dependent organelle movement in squid axoplasm. Nature 356, 722-725). Myosins were found to copurify with these organelles during sucrose gradient fractionation (Bearer, E.L., DeGiorgis, J.A., Bodner, R.A., Kao, A.W., and Reese, T.S. Evidence for myosin motors on organelles in squid axoplasm. Proc Natl Acad Sci USA 90, 11252-11256). Unconventional myosins have been suspected of being organelle motors, while myosin II has been thought to be a contractile myosin involved in mediating actin filament sliding. Indeed, myosin V is suspected of mediating transport of endoplasmic reticulum on actin in axons. Other unidentified myosins appear to be involved in transport of other membrane-bound organelles. To identify other axoplasmic organelle-associated myosins, DeGiorgis et al., in this issue of Molecular Biology of the Cell, take a biochemical approach. Protein biochemistry, peptide sequencing, and PCR-based cloning identifies one axoplasmic myosin of the nonmuscle myosin II class. Surprisingly, myosin II-specific antibodies raised against this myosin demonstrate it is tightly associated with membrane-bound axoplasmic organelles of all sizes. A high proportion (47%) of the total myosin II in axoplasm is organelle-associated even after a 10-min wash in 0.6 M Kl, which dissociates weaker protein-protein bonds. This discovery demonstrates a new role for nonmuscle myosin II and raises exciting questions of myosin isoform versatility and organelle motility.Jennifer Lippincott-Schwartz