Figure 2.

Protein-protein and protein-DNA binding surfaces in the HMG-POU_S-DNA ternary complex. Panel A shows the binding surfaces of the HMG domain. The B0 and C-terminal regions (blue; color image is online) form base-specific contacts with its binding site CTTTGTC and bends the DNA. The S0 region (yellow) forms the protein-protein interface with the POU_S domain. Panel B shows the corresponding DNA-binding site of the HMG domain for sequence-specific binding. Panel C shows the binding surfaces of the POU_S domain. The S region (yellow) forms the protein-protein binding interface with the HMG domain. The B region (blue) consists of key amino acids and forms base-specific contacts with its DNA-binding site. Regions N1 (red) and N2 (green) consist of non-key amino acids and interact with the phosphate groups of DNA. Panel D shows the DNA-binding surfaces for the B, N1, and N2 regions of POU_S using matching colors. The specific sequence ATGC that the B region recognizes is labeled. The phosphate groups P1 and P2 (red) forms at least four hydrogen bonds with the N1 region of the POU_S domain. Phosphate group P3 (green) forms at least two hydrogen bonds with the N2 region of the POU_S domain. This image was rendered by Discovery Studio Visualizer 1.7, Accelrys Inc. (http://accelrys.com/products/discovery-studio/visualization/discovery-studio-visualizer.html).