Fodrin is the general spectrin-like protein found in most cells whereas spectrin and the TW protein have a restricted distribution.

Spectrin and related proteins are made up of a common calmodulin-binding subunit tightly associated with a variant subunit. We have analyzed the distribution of the variant subunits in various cell types using subunit-specific antibodies in immunofluorescence as well as western blotting and in some cases have compared the subunits by two-dimensional peptide mapping. We have found that in the majority of cell types (lymphocytes, hepatocytes, neurons, fibroblasts) fodrin 235 K is present in the absence of the other two variant subunits, spectrin 220 K and TW260. Two cell types were found (skeletal muscle and erythrocytes) which contained only the spectrin variant. Two cell types display two distinct variant subunits. Both fodrin 235 K and spectrin 220 K are detected in cardiac muscle whereas TW260 is present in addition to fodrin 235 K in intestinal epithelial cells. During the early stages of embryonic development of the chicken intestine, fodrin 235 K is expressed in the epithelial cells whereas TW260 and spectrin are not detectable. TW260 is expressed relatively late in development (15-16 days) and is inserted only in the apical (brush border) membrane compartment whereas fodrin 235 K is present in these same cells and underlies the entire plasma membrane. These results suggest that fodrin provides the general linkage system between microfilaments and the membrane in nonerythroid and nonmuscle cells.