The ␣ and ␤ subunits of ␣/␤ heterodimeric integrins function together to bind ligands in the extracellular region and transduce signals across cellular membranes. A possible function for the transmembrane regions in integrin signaling has been proposed from structural and computational data. We have analyzed the capacity of the integrin ␣ 2 , ␣ IIb , ␣ 4 , ␤ 1 , ␤ 3 , and ␤ 7 transmembrane domains to form homodimers and/or heterodimers. Our data suggest that the integrin transmembrane helices

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... n help to stabilize heterodimeric integrins but that the interactions do not specifically associate particular pairs of ␣ and ␤ subunits; rather, the ␣/␤ subunit interaction constrains the extramembranous domains, facilitating signal transduction by a promiscuous transmembrane helix-helix association.