Spindle orientation in Saccharomyces cerevisiae depends on the transport of microtubule ends along polarized actin cables.
Microtubules and actin filaments interact and cooperate in many processes in eukaryotic cells, but the functional implications of such interactions are not well understood. In the yeast Saccharomyces cerevisiae, both cytoplasmic microtubules and actin filaments are needed for spindle orientation. In addition, this process requires the type V myosin protein Myo2, the microtubule end-binding protein Bim1, and Kar9. Here, we show that fusing Bim1 to the tail of the Myo2 is sufficient to orient spindles in the absence of Kar9, suggesting that the role of Kar9 is to link Myo2 to Bim1. In addition, we show that Myo2 localizes to the plus ends of cytoplasmic microtubules, and that the rate of movement of these cytoplasmic microtubules to the bud neck depends on the intrinsic velocity of Myo2 along actin filaments. These results support a model for spindle orientation in which a Myo2-Kar9-Bim1 complex transports microtubule ends along polarized actin cables. We also present data suggesting that a similar process plays a role in orienting cytoplasmic microtubules in mating yeast cells.
Dept. of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA.
Eric
E
Hwang
Justine
J
Kusch
Yves
Y
Barral
Tim C
TC
Huffaker
D008841:Actin Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D008938:Mitosis / Q000502:physiology*; D008954:Models, Biological; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D011993:Recombinant Fusion Proteins; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure
C119683:BIM1 protein, S cerevisiae; D018797:Cell Cycle Proteins; C110443:KAR9 protein, S cerevisiae; D008164:Luminescent Proteins; C077512:MYO2 protein, S cerevisiae; D008868:Microtubule Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D024701:Myosin Type V; D018995:Myosin Heavy Chains