FIGURE 7.

EM analysis of wild-type and MED21(D3K) yeast Mediators. A, a 2D class average from stained images and corresponding diagram showing that the structure and arrangement of head, middle, and tail modules is unaffected by introduction of a FLAG tag at the MED21 C terminus. The approximate position of the D3K mutation is indicated. B, 2D image class averages and corresponding diagrams showing variability in the position of the middle module in yeast Mediator containing MED21(D3K). C, a MED21(D3K) yeast Mediator class average in which the Middle module is well resolved shows that density corresponding to the MED7N-MED31 “knob” is absent. This agrees with what seems to be comparatively weak MED7N-MED31 density in the averages shown in B.