Fig. 4. Effect of III_1c on levels of matrix fibronectin. Fibroblasts were seeded into wells and grown 3 days in the presence of complete medium containing 900 ng/ml ¹²⁵I-labeled fibronectin to obtain a radiolabeled fibronectin matrix. Wells were then washed and monolayers incubated for 16 hours in the presence or absence of 20 µM of various recombinant fibronectin modules as indicated. Cell layers were extracted with 0.5% DOC buffer to obtain DOC-insoluble matrix. An equal proportion of the matrix from each treatment was analyzed by SDS gel electrophoresis under both reducing and nonreducing conditions and visualized by autoradiography. The figure represents one experiment repeated three times.