The minus end-directed motor Kar3 is required for coupling dynamic microtubule plus ends to the cortical shmoo tip in budding yeast.


Journal Article

The budding yeast shmoo tip is a model system for analyzing mechanisms coupling force production to microtubule plus-end polymerization/depolymerization. Dynamic plus ends of astral microtubules interact with the shmoo tip in mating yeast cells, positioning nuclei for karyogamy. We have used live-cell imaging of GFP fusions to identify proteins that couple dynamic microtubule plus ends to the shmoo tip. We find that Kar3p, a minus end-directed kinesin motor protein, is required, whereas the other cytoplasmic motors, dynein and the kinesins Kip2p and Kip3p, are not. In the absence of Kar3p, attached microtubule plus ends released from the shmoo tip when they switched to depolymerization. Furthermore, microtubules in cells expressing kar3-1, a mutant that results in rigor binding to microtubules [2], were stabilized specifically at shmoo tips. Imaging of Kar3p-GFP during mating revealed that fluorescence at the shmoo tip increased during periods of microtubule depolymerization. These data are the first to localize the activity of a minus end-directed kinesin at the plus ends of microtubules. We propose a model in which Kar3p couples depolymerizing microtubule plus ends to the cell cortex and the Bim1p-Kar9p protein complex maintains attachment during microtubule polymerization. In support of this model, analysis of Bim1p-GFP at the shmoo tip results in a localization pattern complementary to that of Kar3p-GFP.

Full Text

Duke Authors

Cited Authors

  • Maddox, PS; Stemple, JK; Satterwhite, L; Salmon, ED; Bloom, K

Published Date

  • August 2003

Published In

Volume / Issue

  • 13 / 16

Start / End Page

  • 1423 - 1428

PubMed ID

  • 12932327

Pubmed Central ID

  • 12932327

Electronic International Standard Serial Number (EISSN)

  • 1879-0445

International Standard Serial Number (ISSN)

  • 0960-9822

Digital Object Identifier (DOI)

  • 10.1016/s0960-9822(03)00547-5


  • eng