Fine structure and distribution of contractile layers inAmoeba proteus preincubated at high temperature

Summary Ultrastructural and immunocytochemical studies allow the localization and identification of a microfilament cortex in heat-shockedAmoeba proteus at different stages of recovery to room temperature. Immediately after heating the cortex is in close contact with the cytoplasmic face of the plasma membrane; however, during cooling it detaches from the membrane and shifts toward the cell centre thus separating a region of peripheral hyaloplasm from central granuloplasm. After polymerization of a new submembrane cortex several detachment and reformation cycles rhythmically repeated for 2–3 hours until a multitude of stratified layers has been formed in the hyaloplasm.Electron micrographs reveal that the cortical layer at the plasma membrane is merely composed of a network of actin filaments, whereas the retracted contractile layers in the hyaloplasm and at the granuloplasmic border contain both, thick and thin filaments often arranged in bundles. The heat-shock induced activities of the microfilament cortex are based on the highly contractile properties of this system in conjunction with controlled displacements in the equilibrium between F- and G-actin.