Figure 6.

Electron density for inhibitors bound in active site of polymerase elongation complex. (A) F_o-F_c (green/red) and 2F_o-F_c (cyan) maps showing clear positive difference density (green) for three compounds in the incoming NTP binding site where they stack on the priming nucleotide and appear to interact with the hydrogen bonding face of the templating base. (B) Results from analogous soaking experiments with the cognate nucleotide showing density for only the cytosine nucleobase, the cytidine nucleoside, and the complete cytidine triphosphate. The inhibitory compounds show density levels that are comparable to those of cytosine and cytidine, but significantly weaker that the difference density observed for the triphosphorylated nucleoside.