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Dynamic instability-the switching of a two-state polymer between phases of steady elongation and rapid shortening-is essential to the cellular function of eukaryotic microtubules, especially during chromosome segregation. Since the discovery of dynamic instability 20 years ago, no other biological polymer has been found to exhibit this behavior. Using total(More)
Ena/VASP proteins regulate the actin cytoskeleton during cell migration and morphogenesis and promote assembly of both filopodial and lamellipodial actin networks. To understand the molecular mechanisms underlying their cellular functions we used total internal reflection fluorescence microscopy to visualize VASP tetramers interacting with static and(More)
BACKGROUND The leading actin network in motile cells is composed of two compartments, the lamellipod and the lamellum. Construction of the lamellipod requires a set of conserved proteins that form a biochemical cycle. The timing of this cycle and the roles of its components in determining actin network architecture in vivo, however, are not well understood.(More)
The Arp2/3 complex, first isolated from Acanthamoeba castellani by affinity chromatography on profilin, consists of seven polypeptides; two actin-related proteins, Arp2 and Arp3; and five apparently novel proteins, p40, p35, p19, p18, and p14 (Machesky et al., 1994). The complex is homogeneous by hydrodynamic criteria with a Stokes' radius of 5.3 nm by gel(More)
Type II par operons harness polymerization of the dynamically unstable actin-like protein ParM to segregate low-copy plasmids in rod-shaped bacteria. In this study, we use time-lapse fluorescence microscopy to follow plasmid dynamics and ParM assembly in Escherichia coli. Plasmids lacking a par operon undergo confined diffusion with a diffusion constant of(More)
Capping protein (CP) is an integral component of Arp2/3-nucleated actin networks that drive amoeboid motility. Increasing the concentration of capping protein, which caps barbed ends of actin filaments and prevents elongation, increases the rate of actin-based motility in vivo and in vitro. We studied the synergy between CP and Arp2/3 using an in vitro(More)
Many cellular structures are assembled from networks of actin filaments, and the architecture of these networks depends on the mechanism by which the filaments are formed. Several classes of proteins are known to assemble new filaments, including the Arp2/3 complex, which creates branched filament networks, and Spire, which creates unbranched filaments. We(More)
Spire and Cappuccino are actin nucleation factors that are required to establish the polarity of Drosophila melanogaster oocytes. Their mutant phenotypes are nearly identical, and the proteins interact biochemically. We find that the interaction between Spire and Cappuccino family proteins is conserved across metazoan phyla and is mediated by binding of the(More)
In addition to its long-studied presence in the cytoplasm, actin is also found in the nuclei of eukaryotic cells. The function and form (monomer, filament, or noncanonical oligomer) of nuclear actin are hotly debated, and its localization and dynamics are largely unknown. To determine the distribution of nuclear actin in live somatic cells and evaluate its(More)
Most eukaryotic cells express multiple isoforms of the actin-binding protein tropomyosin that help construct a variety of cytoskeletal networks. Only one nonmuscle tropomyosin (Tm1A) has previously been described in Drosophila, but developmental defects caused by insertion of P-elements near tropomyosin genes imply the existence of additional, nonmuscle(More)