This review describes available data on the structure of viral RNA-dependent RNA polymerases (RdRP) obtained from X-ray analysis and discusses the functional significance of the structural elements of these enzymes. Because most of the studies done to date relate to RdRP structures of picorna-, flavi-, and caliciviruses, here we consider mostly the structures of RdRP of these groups of viruses, and also include information about polymerases of other virus families.

The activities of wild-type mengovirus RNA polymerase (RdRP) and of its three mutants with C-terminal tryp-tophan residue replaced by residues of alanine (W460A), phenylalanine (W460F), or tyrosine (W460Y) were studied. The proteins were expressed in E. coli and purified by affinity chromatography with the IMPACT system. The isolated recombinant proteins were studied using a cell-free replication system on elongation of oligo(U) primer on RNA template corresponding to the 3′-terminal 366-meric fragment of the mengovirus RNA. The activities of the mutant polymerases were comparable to that of the wild-type enzyme.