A Structure-Function Diversity Survey of the RNA-Dependent RNA Polymerases From the Positive-Strand RNA Viruses

Jia, Hengxia; Gong, Peng

Viral RdRPs represent a unique nucleic acid polymerase class of and is the only class that does not involve DNA in any stages of the synthesis. To preserve their RNA template and ribonucleotide triphosphate (rNTP) substrate specificity, the seven catalytic motifs are the central segments to preserve during virus evolution. While we have mainly focused on the diversity and variations beyond the catalytic modules, attentions may also be drawn to the variations within the catalytic module but excluding the catalytic motifs. For the representative RdRPs that we surveyed in this study, the spacing between certain catalytic motifs could vary to a great extent. For example, the residue distance between the conserved motif B serine and the motif C aspartic acid in these RdRPs ranges from 30 to 94, corresponding to a motif spacing of 12-76 residues (Figures 1, 2) . We hypothesize that such regions, if located at or near the RdRP protein surface, may have been utilized by the positive-strand RNA viruses as evolutionary "hot spot, " in particular in their host adaptation processes. Further investigations are needed to test this hypothesis.