Association of mutant GP Ibα with GP Ibβ. GP Ibβ was immunoprecipitated from cell lysates of stably transfected cells (see Fig 6). The samples were reduced, electrophoresed on a 7.5% SDS-polyacrylamide gel, and transferred to nitrocellulose membrane. The membrane was analyzed for GP Ibα content with WM-23. βIX, untransfected CHO βIX cells; other labeling as in Fig 6.