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 genetically with type I myosins. While deletion of BZZ1 shows no obvious phenotype, simultaneous deletion of the BZZ1 , MYO3 , and MYO5 genes is lethal. Overexpression of Bzz1p inhibits cell growth, and a bzz1 Δ myo5 Δ double mutant is unable to restore actin polarity after NaCl stress. Finally, Bzz1p in vitro is able to recruit a functional actin polymerization machinery through its SH3 domains. Its interactions with Las17p, Vrp1p, and the type I myosins are essential for this process. This suggests that Bzz1p could be implicated in the regulation of actin polymerization.
Soulard, A., Lechler, T., Spiridonov, V., Shevchenko, A., Shevchenko, A., Li, R., & Winsor, B. (2002). Saccharomyces cerevisiae Bzz1p Is Implicated with Type I Myosins in Actin Patch Polarization and Is Able To Recruit Actin-Polymerizing Machinery In Vitro. Molecular and Cellular Biology, 22(22), 7889–7906. https://doi.org/10.1128/mcb.22.22.7889-7906.2002