The fibronectin molecule consists of repeating globular domains with specific cell-binding sites for interactions with integrins. Four of the fibronectin peptide sites (abbreviated using the single-letter code for amino acids) that can interact with specific integrins are shown extending down toward the integrins. Integrins contain one α and one β subunit, which span the plasma membrane and terminate in short cytoplasmic domains that are thought to mediate intracellular signaling.