Highly similar structural frames link the template tunnel and NTP entry tunnel to the exterior surface in RNA-dependent RNA polymerases

Lang, Dorothy M.; Zemla, A. T.; Zhou, C. L. Ecale

The tertiary structure of the hmE is illustrated in Figure 9B and C. Most of the homomorph is at the exterior of the protein near the NTP entry tunnel. Although it has extensive surface exposure, each terminus of the homomorph appears to be anchored by residues that are not part of the homomorph; as a result, the terminal residue at each end of the homomorph is exposed as a single residue at the exterior surface of the protein. Motif E is located near the N-terminal edge of the homomorph and contacts the surface of the NTP entry tunnel (2) . The C-terminal segment of the homomorph is folded back on itself in a manner that places the speciesspecific loop at the surface of the protein ( Figure 8C) . The homomorph forms a double strand through PV_M392, at which point the remainder of the homomorph is a single-stranded helix that emerges at the exterior surface of the protein. In PV, the C-terminal of hmE (R402) is exposed at the surface the protein and surrounded by the segment 28-SAFHYVFEG-36.