The Tails of Two Myosins

Two papers in this issue of The Journal of Cell Biology uncover a possible new connection between the actin-nucleating complex of proteins, the Arp2/3 complex, and the type I myosin motors. In this issue, Lechler et al. 2000 and Evangelista et al. 2000 show a direct interaction of the S. cerevisiae myosin I motors (Myo3p and Myo5p) with the Arp2/3 complex through an acidic COOH-terminal sequence motif. The data suggest that a large complex containing both myosin motors and actin nucleating proteins may be a functional unit for signal-induced actin assembly. Furthermore, both studies provide evidence that myosin I function is essential for assembly and maintenance of filamentous actin structures in cells. This is exciting and raises some controversy, given the recent discovery that intracellular pathogens such as Shigella flexnerii and Listeria monocytogenes do not use myosin motors...