Fig. 7.

RNA Pol II ChIP time course in ES and MEF cells and model for ELK1 AD interaction with MED23. ChIP for Pol II at the Egr1 promoter (A) and ~4 kb downstream (B) in ES (white) and MEF (black) WT and KO cells. Background signal with preimmune IgG for WT cells at time 0 is shown. Samples were quantitated by real-time PCR and normalized to percent of input chromatin. Cells were starved and 20% FBS was added for 0, 5, 20, or 40 min before cross-linking. Error bars indicate SDs from three independent experiments. (C) Model for ELK1 AD interaction with MED23. The ELK1 IHFW sequence makes a hydrophobic interaction with MED23 (light blue) that provides much of the energy for mediator binding. MED23 interactions with phosphates added to the ELK1 regulatory serines by a MAPK enhance binding directly and also induce a conformational change in MED23 (light green) that stabilizes this interaction. This conformational change also results in increased binding of Pol II to the Egr1 promoter and an increase in the percentage of Pol II molecules that transcribe away from the promoter region.