Figure 6. Position of TFIIK and CTD and Stimulation of CTD Phosphorylation
(A) Position of TFIIK density in the Med-PIC structure. TFIIK difference density calculated by subtraction of core Med-Pol II and PIC maps from the Med-PIC
structure (Figure S7and Integrative Molecular Modeling Studies inSTAR Methods) is shown after filtration and at the appropriate map threshold (orange density).
(B) Integrative modeling reveals TFIIK subunit localizations (solid transparent density) within the Med-PIC EM map (blue mesh) that are consistentwith the
calculated TFIIK difference density and cross-links between TFIIK and Rad3 surface lysine residues (red spheres). Model color scheme: Rad3, pink; Tfb3, yellow;
Kin28, beige; Ccl1, blue.
(C) Model for the path of the CTD through the initiation complex. The CTD path is constrained by multiple anchor points provided by pol II and CTD-Med Head
crystal structures, positioning the CTD kinase (Kin28) and cross-links obtained between a C-terminal CTD and N-terminal Med19 lysine residues (Plaschka et al.,
2015; Robinson et al., 2015)(Figure S3A).
(D) Close association between the Med7N-31 and Neck domain of the Head module at the Head-Middle interface forms a CTD channel that directs the CTD
toward interaction with TFIIK. The stimulation of CTD phosphorylation by Mediator is explained by the role of Mediator in positioning both TFIIK and CTD for
interaction. See alsoFigure S7.
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