Cells synchronized at the G1/S boundary were released back into the cell cycle and treated in the presence of absence of PMA (0.1 µm, 7 h after G1/S release), U0126 (10 µm, 6.5 h after G1/S release), or PMA and U0126 together. (a) Immunoblot analysis of ppERK1/2 (top panel), cyclin B1 (middle panel), and α-tubulin (lower panel) as a protein loading control. (b) The MI at varying times after G1/S release in untreated (white bars), PMA-treated (black bars), U0126-treated (checkered bars), or PMA- and U0126- treated cells (grey bars). Data represent the mean and standard error from three independent experiments.