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Vol. 16, Issue 1, 238-247, January 2005

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Cellular Distribution and Functions of Wild-Type and Constitutively Activated Dictyostelium PakB

Marc de la Roche ^*, Amjad Mahasneh ^* , Sheu-Fen Lee ^*, Francisco Rivero , and Graham P. Côté ^* 

^* Department of Biochemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6; Zentrum für Biochemie, Medizinische Fakultät, Universität zu Köln, 50931 Köln, Germany

Submitted June 29, 2004; Revised September 4, 2004; Accepted October 12, 2004
Monitoring Editor: Peter Devreotes

Dictyostelium PakB, previously termed myosin I heavy chain kinase, is a member of the p21-activated kinase (PAK) family. Two-hybrid assays showed that PakB interacts with Dictyostelium Rac1a/b/c, RacA (a RhoBTB protein), RacB, RacC, and RacF1. Wild-type PakB displayed a cytosolic distribution with a modest enrichment at the leading edge of migrating cells and at macropinocytic and phagocytic cups, sites consistent with a role in activating myosin I. PakB fused at the N terminus to green fluorescent protein was proteolyzed in cells, resulting in removal of the catalytic domain. C-terminal truncated PakB and activated PakB lacking the p21-binding domain strongly localized to the cell cortex, to macropinocytic cups, to the posterior of migrating cells, and to the cleavage furrow of dividing cells. These data indicate that in its open, active state, the N terminus of PakB forms a tight association with cortical actin filaments. PakB-null cells displayed no significant behavioral defects, but cells expressing activated PakB were unable to complete cytokinesis when grown in suspension and exhibited increased rates of phagocytosis and pinocytosis.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Department of Biotechnology and Genetic Engineering, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan.

Corresponding author. E-mail address: coteg{at}post.queensu.ca.

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