Prior to matrix formation, fibronectin (FN1) exists as a protein dimer. Often the two peptide chains are differentially-spliced variants. The chains are linked by a pair of C-terminal disulfide bonds which are essential for subsequent multimerization (Schwarzbaur 1991). FN1 monomers have a molecular weight of 230-270 kDa depending on the alternative splicing and contain three types of repeating domains, type I, II, and III. Type I and II domains are stabilized by intra-chain disulfide bonds. FN1 dimer binding to alpha5beta1 integrin stimulates self-association.