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© The Rockefeller University Press, 0021-9525/1997//375 $5.00
The Journal of Cell Biology, Volume 138, Number 2, , 1997 375-384

Article

The Human Arp2/3 Complex Is Composed of Evolutionarily Conserved Subunits and Is Localized to Cellular Regions of Dynamic Actin Filament Assembly



Matthew D. Welch*, Angela H. DePace{ddagger}, Suzie Verma*, Akihiro Iwamatsu§, and Timothy J. Mitchison*

* Department of Cellular and Molecular Pharmacology, {ddagger} Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0450; and § Central Laboratories for Key Technology, Kirin Brewery Company, Ltd., Yokohama, Japan

The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of seven subunits which include the actin related proteins Arp2 and Arp3, and five others referred to as p41-Arc, p34-Arc, p21-Arc, p20-Arc, and p16-Arc (Arp complex). We have determined the predicted amino acid sequence of all seven subunits. Each has homologues in diverse eukaryotes, implying that the structure and function of the complex has been conserved through evolution. Human Arp2 and Arp3 are very similar to family members from other species. p41-Arc is a new member of the Sop2 family of WD (tryptophan and aspartate) repeat–containing proteins and may be posttranslationally modified, suggesting that it may be involved in regulating the activity and/or localization of the complex. p34-Arc, p21-Arc, p20-Arc, and p16-Arc define novel protein families. We sought to evaluate the function of the Arp2/3 complex in cells by determining its intracellular distribution. Arp3, p34-Arc, and p21-Arc were localized to the lamellipodia of stationary and locomoting fibroblasts, as well to Listeria monocytogenes assembled actin tails. They were not detected in cellular bundles of actin filaments. Taken together with the ability of the Arp2/3 complex to induce actin polymerization, these observations suggest that the complex promotes actin assembly in lamellipodia and may participate in lamellipodial protrusion.

Abbreviations used in this paper: CBS, cytoskeleton buffer with sucrose; dbEST, database of expressed sequence tags; EGFP and GFP, green fluorescent protein; GST, glutathione S-transferase; PH, pleckstrin homology.

We want to thank all of the members of the Mitchison lab, and especially Louise Cramer, Arshad Desai, Aneil Mallavarapu, Jody Rosenblatt, Jack Taunton and Claire Walczak for many helpful discussions and for critically reading the manuscript. We also want to thank Dirk Winter and Rong Li for sharing sequence information before publication.

Please address all correspondence to Matthew D. Welch, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143-0450. Tel.: (415) 476-0836. Fax: (415) 476-5233. e-mail: welch{at}cgl.ucsf.edu


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