The S77A RARα mutant inhibits proliferation of SCC25 cells. G418 resistant (neo), wild type HA-tagged RARα (HA1,2), and S77A mutant clones (RAR1-4) were cultured as described in Methods. At two day intervals, the cells in triplicate cultures were counted with a hemacytometer. These experiments were performed three times with similar results. Error bars indicate SEM.