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

Within the N-terminal side of the homomorph, at the edge of the motif (PV 226-227), there is a minor discontinuity in structure homology ( Figure 4A ). The distance between the discontinuities in each species is provided in a column within the figure (white) that indicates the entire span over which discontinuity exists for each species. However, the loop represented by this discontinuity varies in length by only one to four amino acids. Figure 4B illustrates the tertiary structure of the hmA. Each end of the homomorph is at the exterior surface of the protein (Figure 4C ), and its center-the conserved Motif A-is at the surface of the template tunnel. The overall configuration of the homomorph is spring-like ( Figure 4D ). The species-specific loop within the homomorph is located at the exterior of the protein.