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. Author manuscript; available in PMC: 2015 Jun 5.
Published in final edited form as: Cell. 2014 May 29;157(6):1430–1444. doi: 10.1016/j.cell.2014.05.015

Figure 6. yMED conformational rearrangements and RNAPII interaction.

Figure 6

(A) The Head-Middle and Head-Tail module interfaces in yMED appear to be critical for control of yMED conformation. CTD binding at the Head-Middle interface, and targeting of the Head-Tail interface by activators could help explain how yMED conformation is controlled.

(B) Examples of large-scale conformational changes triggered by changes at yMED module interfaces. Tagging or deletion of Med31 destabilizes the contact between the Middle and Head modules (top panels). The Head and Tail modules can interact in the absence of the Middle module, as evidenced in a class average calculated from Med19Δ yMED images (bottom left), but deletion of Med18 (and concomitant loss of Med20) destabilizes the contact between the Head jaws and the Med2-Med3-Med15 connector to the Tail (bottom right). Dashed lines in the schematics represent the altered position of the Head module in corresponding class averages. Scale bar corresponds to 10 nm.

(C) Rigid docking of yMED modules into a published EM map of the yMED-RNAPII-TFIIF holoenzyme (Davis et al., 2002) accounts for all yMED density in the holoenzyme map (shown in mesh) and illustrates the conformational changes required for interaction of yMED with polymerase. A concerted rotation of the Head and Middle modules opens a site for RNAPII binding and the Tail rotates as observed after yMED incubation with Gcn4. Scale bar corresponds to 10 nm.

(D) yMED module rearrangements triggered by incubation with a recombinant GST-CTD. The distribution of yMED particles amongst various conformations (indicated by the bars) shifts considerably after yMED interaction with the CTD, with the Head and Middle modules rotating away from their respective positions in the predominant conformation for yMED alone.

(E) yMED module rearrangements triggered by incubation with a recombinant GST-Gcn4 yeast activator. The activator triggers a change in the conformation of the Med2-Med3-Med15 connector, which results in rotation of the Tail module. See also Figure S6.