Tropomyosin-containing actin cables direct the Myo2p-dependent polarized delivery of secretory vesicles in budding yeast.
The actin cytoskeleton in budding yeast consists of cortical patches and cables, both of which polarize toward regions of cell growth. Tropomyosin localizes specifically to actin cables and not cortical patches. Upon shifting cells with conditionally defective tropomyosin to restrictive temperatures, actin cables disappear within 1 min and both the unconventional class V myosin Myo2p and the secretory vesicle-associated Rab GTPase Sec4p depolarize rapidly. Bud growth ceases and the mother cell grows isotropically. When returned to permissive temperatures, tropomyosin-containing cables reform within 1 min in polarized arrays. Cable reassembly permits rapid enrichment of Myo2p at the focus of nascent cables as well as the Myo2p- dependent recruitment of Sec4p and the exocyst protein Sec8p, and the initiation of bud emergence. With the loss of actin cables, cortical patches slowly assume an isotropic distribution within the cell and will repolarize only after restoration of cables. Therefore, actin cables respond to polarity cues independently of the overall distribution of cortical patches and are able to directly target the Myo2p-dependent delivery of secretory vesicles and polarization of growth.
Pruyne
D W
DW
Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853, USA.
Schott
D H
DH
Bretscher
A
A
D008841:Actin Cytoskeleton / Q000502:physiology*; D000199:Actins / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D016764:Cell Polarity; D005089:Exocytosis / Q000502:physiology*; D005656:Fungal Proteins / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D018995:Myosin Heavy Chains; D024462:Myosin Type II; D024701:Myosin Type V; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology*; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D014335:Tropomyosin / Q000235:genetics / Q000502:physiology*; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins
D000199:Actins; D002352:Carrier Proteins; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; C077512:MYO2 protein, S cerevisiae; C434211:MYO2 protein, S pombe; D020033:Protein Isoforms; C489603:SEC8 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D014335:Tropomyosin; D033921:Vesicular Transport Proteins; C489604:sec8 protein, S pombe; D019204:GTP-Binding Proteins; D024462:Myosin Type II; D024701:Myosin Type V; C064320:SEC4 protein, S cerevisiae; D018995:Myosin Heavy Chains; D020691:rab GTP-Binding Proteins