How to analyze electron micrographs of rafts of actin filaments crosslinked by actin-binding proteins.

Actin bundles are common cytoskeletal structures but ones which are usually polymorphic, varying from bundle to bundle. Two-dimensional arrays of actin filaments crosslinked by actin-bundling proteins are more tractable structures to analyze than are the three-dimensional bundles found in cells. The first step in analyzing these two-dimensional "rafts" is to determine the spatial relationships between neighboring filaments. It is difficult to discern such relationships by inspection of the electron micrographs of rafts, but easy by examination of the Fourier transforms. We provide theory and examples of the analysis of transforms of rafts, and show that different bundling proteins give rise to different kinds of rafts. Copyright 1998 Academic Press Limited.