Procedure for the purification of the fibronectin proteolytic fragments containing the ED-B oncofetal domain.

Fibronectin (FN) is the blend of structurally different molecules (isoforms) whose makeup varies depending on the FN sources. Fibronectin polymorphism is caused by three sequences (called ED-A, ED-B, and IIICS) which may be included or excluded from the FN molecule depending on the alternative splicing patterns of a single primary transcript. The sequence ED-B, which is a complete type III repeat of 91 amino acids, presents some interesting peculiarities: it is the most conserved FN region and, in normal adult tissues, the ED-B-containing FN has an extremely restricted distribution while having a much greater expression in fetal and tumor tissues (Carnemolla et al., 1989, J. Cell Biol. 108, 1139-1148), suggesting that the ED-B sequence may confer to the FN molecules specific biological activities required during ontogenesis and oncogenetic processes. Here we describe a detailed procedure to purify fibronectin fragments containing the ED-B sequence. These purified fragments are useful reagents in the study of the biological function(s) of the ED-B-containing FN molecules.