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

Motif C is not a component of a larger structurally conserved segment, but has the same key features of the other homomorphs. It is folded in a manner that places the apex of the fold at the wall of the template tunnel, and both the N-terminus and C-terminus at the exterior surface of the protein ( Figure 6B and C) . Therefore, Motif C as defined in the literature comprises the homomorph. The absence of R2R correspondence adjacent to hmC indicates that the structures of the adjacent sequence segments are highly specific to each species. HmC is highly conserved in the RdRps and highly similar to the DNA-dependent polymerases. Although there is a sequence inversion in the birnaviruses (Motif C precedes Motif A), Figure 7B and C illustrates that despite the difference in sequence order, the homomorphs occupy a similar tertiary position. StralSV analysis indicates that the structure of Motif C is highly conserved in the RNA-dependent polymerases, though slightly different in the DNA-dependent polymerases ( Figure 6A ).