Direct involvement of yeast type I myosins in Cdc42-dependent actin polymerization (original) (raw)
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Molecular and cellular biology, 2002
In Saccharomyces cerevisiae, the WASP (Wiskott-Aldrich syndrome protein) homologue Las17p (also called Bee1p) is an important component of cortical actin patches. Las17p is part of a high-molecular-weight protein complex that regulates Arp2/3 complex-dependent actin polymerization at the cell cortex and that includes the type I myosins Myo3p and Myo5p and verprolin (Vrp1p). To identify other factors implicated with this complex in actin regulation, we isolated proteins that bind to Las17p by two-hybrid screening and affinity chromatography. Here, we report the characterization of Lsb7/Bzz1p (for Las seventeen binding protein 7), an Src homology 3 (SH3) domain protein that interacts directly with Las17p via a polyproline-SH3 interaction. Bzz1p coimmunoprecipitates in a complex with Las17p, Vrp1p, Myo3/5p, Bbc1p, Hsp70p, and actin. It colocalizes with cortical actin patches and with Las17p. This localization is dependent on Las17p, but not on F-actin. Bzz1p interacts physically and ge...
A role for myosin-I in actin assembly through interactions with Vrp1p, Bee1p, and the Arp2/3 complex
The Journal of cell biology, 2000
Type I myosins are highly conserved actin-based molecular motors that localize to the actin-rich cortex and participate in motility functions such as endocytosis, polarized morphogenesis, and cell migration. The COOH-terminal tail of yeast myosin-I proteins, Myo3p and Myo5p, contains an Src homology domain 3 (SH3) followed by an acidic domain. The myosin-I SH3 domain interacted with both Bee1p and Vrp1p, yeast homologues of human WASP and WIP, adapter proteins that link actin assembly and signaling molecules. The myosin-I acidic domain interacted with Arp2/3 complex subunits, Arc40p and Arc19p, and showed both sequence similarity and genetic redundancy with the COOH-terminal acidic domain of Bee1p (Las17p), which controls Arp2/3-mediated actin nucleation. These findings suggest that myosin-I proteins may participate in a diverse set of motility functions through a role in actin assembly.
The Yeast V159N Actin Mutant Reveals Roles for Actin Dynamics In Vivo
The Journal of Cell Biology, 1998
Actin with a Val 159 to Asn mutation (V159N) forms actin filaments that depolymerize slowly because of a failure to undergo a conformational change after inorganic phosphate release. Here we demonstrate that expression of this actin results in reduced actin dynamics in vivo, and we make use of this property to study the roles of rapid actin filament turnover. Yeast strains expressing the V159N mutant ( act1-159 ) as their only source of actin have larger cortical actin patches and more actin cables than wild-type yeast. Rapid actin dynamics are not essential for cortical actin patch motility or establishment of cell polarity. However, fluid phase endocytosis is defective in act1-159 strains. act1-159 is synthetically lethal with cofilin and profilin mutants, supporting the conclusion that mutations in all of these genes impair the polymerization/ depolymerization cycle. In contrast, act1-159 partially suppresses the temperature sensitivity of a tropomyosin mutant, and the loss of cytoplasmic cables seen in fimbrin, Mdm20p, and tropomyosin null mutants, suggesting filament stabilizing functions for these actin-binding proteins. Analysis of the cables in these double-mutant cells supports a role for fimbrin in organizing cytoplasmic cables and for Mdm20p and tropomyosin in excluding cofilin from the cables.
Developmental Cell, 2006
Actin polymerization essential for endocytic internalization in budding yeast is controlled by four nucleation promoting factors (NPFs) that each exhibits a unique dynamic behavior at endocytic sites. How each NPF functions and is regulated to restrict actin assembly to late stages of endocytic internalization is not known. Quantitative analysis of NPF biochemical activities, and genetic analysis of recruitment and regulatory mechanisms, defined a linear pathway in which protein composition changes at endocytic sites control actin assembly and function. We show that yeast WASP initiates actin assembly at endocytic sites and that this assembly and the recruitment of a yeast WIP-like protein by WASP recruit a type I myosin with both NPF and motor activities. Importantly, type I myosin motor and NPF activities are separable, and both contribute to endocytic coat inward movement, which likely represents membrane invagination. These results reveal a mechanism in which actin nucleation and myosin motor activity cooperate to promote endocytic internalization.
Yeast actin-binding proteins: evidence for a role in morphogenesis
The Journal of Cell Biology, 1988
Three yeast actin-binding proteins were identified using yeast actin filaments as an affinity matrix. One protein appears to be a yeast myosin heavy chain; it is dissociated from actin filaments by ATP, it is similar in size (200 kD) to other myosins, and antibodies directed against Dictyostelium myosin heavy chain bind to it. Immunofluorescence experiments show that a second actin-binding protein (67 kD) colocalizes in vivo with both cytoplasmic actin cables and cortical actin patches, the only identifiable actin structures in yeast. The cortical actin patches are concentrated at growing surfaces of the yeast cell where they might play a role in membrane and cell wall insertion, and the third actin-binding protein (85 kD) is only detected in association with these structures. This 85-kD protein is therefore a candidate for a determinant of growth sites. The in vivo role of this protein was tested by overproduction; this overproduction causes a reorganization of the actin cytoskelet...