PURE THOUGHTS WITH IMPURE PROTEINS - PERMEABILIZED CELL MODELS OF ORGANELLE MOTILITY

Permeabilized cell models provide an experimental middle ground wherei n the in vitro properties of mechanochemical proteins can be reconcile d with the physical and topological constraints of the intact cell. Se veral well-studied examples of organelle motility are described here, including the actin-based cytoplasmic streaming of Characean algae, th e microtubule-based aggregation and dispersion of pigment granules in chromatophores and the saltatory movements of vesicles along microtubu les in fibroblasts and macrophages. The permeabilized models developed for these systems have helped to integrate observations in vivo with in vitro assays of motor proteins.