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* Department of Biochemistry and Molecular Biology, The Milton S. Hershey Medical Center, The Pennsylvania State
University, Hershey, Pennsylvania 17033; and Yeast verprolin, encoded by VRP1, is implicated in cell growth, cytoskeletal organization, endocytosis and mitochondrial protein distribution and function. We show that verprolin is also required for bipolar
bud-site selection. Previously we reported that additional actin suppresses the temperature-dependent
growth defect caused by a mutation in VRP1. Here we
show that additional actin suppresses all known defects
caused by vrp1-1 and conclude that the defects relate to
an abnormal cytoskeleton. Using the two-hybrid system, we show that verprolin binds actin. An actin-binding domain maps to the LKKAET hexapeptide located
in the first 70 amino acids. A similar hexapeptide in
other acting-binding proteins was previously shown to
be necessary for actin-binding activity. The entire 70- amino acid motif is conserved in novel higher eukaryotic proteins that we predict to be actin-binding, and
also in the actin-binding proteins, WASP and N-WASP.
Verprolin-GFP in live cells has a cell cycle-dependent
distribution similar to the actin cortical cytoskeleton. In
fixed cells hemagglutinin-tagged Vrp1p often co-localizes with actin in cortical patches. However, disassembly of the actin cytoskeleton using Latrunculin-A does
not alter verprolin's location, indicating that verprolin
establishes and maintains its location independent of
the actin cytoskeleton. Verprolin is a new member of
the actin-binding protein family that serves as a polarity
development protein, perhaps by anchoring actin. We
speculate that the effects of verprolin upon the actin cytoskeleton might influence mitochondrial protein sorting/function via mRNA distribution.
The Department of Biochemistry, University of Louisville Medical School,
Louisville, Kentucky 40292
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