Actin-based gelation of cytoplasmic extracts from brain tissue

Incubation of rat brain cytoplasmic extracts under the conditions described in this paper results in the formation of three-dimensional gels. Ultrastructurally, these gels correspond to complex supramolecular structures formed by single microfilaments and by microfilament bundles. Analysis of protein composition indicates that cytoplasmic gels are composed of actin and several associated proteins. Among the latter class of components, we have identified polypeptides with molecular weights of 55,000 (55K), 140,000 (140K), and a set of two or three polypeptides with molecular weights in the range of 235,000-245,000 (235-245K). The 55K and 140K components do not seem to correspond to any previously identified actin-associated proteins, while the 235-245K polypeptides may correspond to the protein known as fodrin.