Diagram of recombinant proteins containing the five different splice variants of the HepII/IIICS region obtained by RT-PCR expression cloning. The 3′ primer was complementary to the end of the 15th type III repeat and the 5′ primer to the start of the 12th type III repeat of human fibronectin. The full-length fibronectin subunit is shown together with the alternatively spliced IIICS region, which is represented as the open box. The numbers assigned to the H variants refer to the number of amino acids in the IIICS. The locations of the three recognition sequences for α₄β₁, HI, CSI, and CS5, are indicated. Note that H120 contains all three sites and H0 contains HI alone.