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© The Rockefeller University Press, 0021-9525/1999//83 $5.00
The Journal of Cell Biology, Volume 144, Number 1, , 1999 83-98


Article

Coronin Promotes the Rapid Assembly and Cross-linking of Actin Filaments and May Link the Actin and Microtubule Cytoskeletons in Yeast



Bruce L. Goode*, Jonathan J. Wong*, Anne-Christine Butty{ddagger}, Matthias Peter{ddagger}, Ashley L. McCormack§, John R. Yates§, David G. Drubin*, and Georjana Barnes*

* Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202; {ddagger} Swiss Institute for Experimental Cancer Research, Lausanne, Switzerland; and § Department of Molecular Biotechnology, University of Washington, Seattle, Washington 98195

Coronin is a highly conserved actin-associated protein that until now has had unknown biochemical activities. Using microtubule affinity chromatography, we coisolated actin and a homologue of coronin, Crn1p, from Saccharomyces cerevisiae cell extracts. Crn1p is an abundant component of the cortical actin cytoskeleton and binds to F-actin with high affinity (Kd 6 x 10–9 M). Crn1p promotes the rapid barbed-end assembly of actin filaments and cross-links filaments into bundles and more complex networks, but does not stabilize them. Genetic analyses with a crn1{Delta} deletion mutation also are consistent with Crn1p regulating filament assembly rather than stability. Filament cross-linking depends on the coiled coil domain of Crn1p, suggesting a requirement for Crn1p dimerization. Assembly-promoting activity is independent of cross-linking and could be due to nucleation and/or accelerated polymerization. Crn1p also binds to microtubules in vitro, and microtubule binding is enhanced by the presence of actin filaments. Microtubule binding is mediated by a region of Crn1p that contains sequences (not found in other coronins) homologous to the microtubule binding region of MAP1B. These activities, considered with microtubule defects observed in crn1{Delta} cells and in cells overexpressing Crn1p, suggest that Crn1p may provide a functional link between the actin and microtubule cytoskeletons in yeast.

Key Words: actin • microtubule • coronin • cytoskeleton • yeast



Abbreviations used in this paper: GFP, green fluorescent protein; GST, glutathione-S-transferase; HSS, high speed supernatant; IPTG, isopropyl-thio-β-D-galactoside.

Address correspondence to Dr. Georjana Barnes, Department of Molecular and Cell Biology, 401 Barker Hall, University of California, Berkeley, CA 94720-3202. Tel.: (510) 643-2010. Fax: (510) 642-6420. E-mail: gbarnes @socrates.berkeley.edu

We are especially grateful to Lisa Belmont for making the initial observation of the genetic interactions between the crn1{Delta} and act1-159 mutations. We also thank Alison Adams for generously providing purified Sac6p, Hadar Haddad for technical assistance, Kent McDonald for instruction and assistance with electron microscopy, and Lisa Belmont, Pekka Lappalainen, Jamie Cope, and Keith Kozminski for helpful comments on the manuscript.



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