1 The Yeast Cytoskeleton

Abstract

INTRODUCTION
An internal cytoskeleton consisting of a network of protein polymer filaments is a common feature of all eukaryotic cells. The cytoskeleton serves to organize the cytoplasm, to provide the means for generating force within the cell, and to determine and maintain the shape of the cell and its structural integrity. Three different types of cytoskeletal filaments are found. One type is based on long flexible polymers of actin called microfilaments (5–7 nm in diameter), another is based on more rigid polymers of tubulin called microtubules (hollow tubes 25 nm in diameter), and the third type is based on polymers of any of a number of related fibrous coiled-coil proteins called intermediate filaments (~10 nm in diameter). The microfilaments and microtubules of Saccharomyces cerevisiae closely resemble those of animal cells, and the structure and functions of these cytoskeletal elements have been extensively studied in this yeast (Botstein 1986; Huffaker et al. 1987; Drubin 1989; Stearns 1990; Welch et al. 1994; Cid et al. 1995). Potential nuclear lamins and 10-nm filament structures have also been reported in Saccharomyces, but relatively little is known about the structure and functions of intermediate filaments in yeast (Haarer and Pringle 1987; Kim et al. 1991; Chant 1996).

The cytoskeleton is a complex architecture of polymers and associated proteins that plays a part in many aspects of cellular physiology. Understanding the elaborate system of interactions upon which cytoskeletal function is based requires tools that can be used on the intact organism. Indeed, much of what...