Figure 4.
Three stereo images showing the BS regions. The colour code is green for the H4′ docking sequence, red for the H2A docking sequence and sky blue for key waters. (a) shows the key waters of the BS region in the HO. (b) shows the same area of the NCP after it has been aligned with the HO. Note the good match in water positions between the two figures and the hydrophobic channel between the two docking sequences. This is the primary site (and equivalently the H4–H2A′ docking sequence) that needs to be disrupted before RNA polymerase II-mediated transcription can proceed. (c) shows the 2F o − F c electron density around the BS region (contoured to 3σ, 0.45 e Å−3, values are from COOT; Emsley & Cowtan, 2004 ▶).