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

HmG is shared by picornaviruses, caliciviruses and flaviviruses, although the structures of each of these groups begin to diverge within the C-terminal segment of Motif G. Motif G is characterized by the conserved motif [T/Sx 1-2 G], which is located near the outer edge of the template tunnel. The motif may enforce the correct orientation of essential residues and a primer (35) . Each flank of the homomorph contains amino acid residues that significantly affect the life cycle of the species. In PV, mutations at the N-terminal residue of the homomorph (D71A/E72A) are lethal (37) . Mutations located outside the N-terminal edge of the motif (PV D105A/E108A) result in small plaques (37) . Downstream from the C-terminal edge of the motif, there is a nuclear localization signal (NLS) in the picornaviruses and caliciviruses. The NLS is located two residues from the C-terminus of the homomorph and mutations in the NLS (K125A/ K126A/K127A and K127A/R128A/D129A) are lethal to PV (37) .