UNLABELLED The negative-sense RNA genome of influenza A virus is transcribed and replicated by the viral RNA-dependent RNA polymerase (RdRP). The viral RdRP is an important host range determinant, indicating that its function is affected by interactions with cellular factors. However, the identities and the roles of most of these factors remain unknown. Here, we employed affinity purification f...

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, has been a global concern. While there have some vaccines and drugs, rapid emergence of variants due to mutations threatened public health. As de novo drug development process is expensive time-consuming, repurposing existing antiviral drugs against SARS-CoV-2 an alternative promising approach miti...

All plus-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRp) that functions as the catalytic subunit of the viral replication/transcription complex, directing viral RNA synthesis in concert with other viral proteins and, sometimes, host proteins. RNA synthesis essentially can be initiated by two different mechanisms, de novo initiation and primer-dependent initiation. Most viral Rd...

The objective of this study was to identify the active form of the feline calicivirus (FCV) RNA-dependent RNA polymerase (RdRP). Multiple active forms of the FCV RdRP were identified. The most active enzyme was the full-length proteinase-polymerase (Pro-Pol) precursor protein, corresponding to amino acids 1072 to 1763 of the FCV polyprotein encoded by open reading frame 1 of the genome. Deletio...

The Sabin I poliovirus live, attenuated vaccine strain encodes for four amino acid changes (i.e., D53N, Y73H, K250E, and T362I) in the RNA-dependent RNA polymerase (RdRp). We have previously shown that the T362I substitution leads to a lower fidelity RdRp, and viruses encoding this variant are attenuated in a mouse model of poliovirus. Given these results, it was surprising that the nucleotide ...

Extracts of vacuole-depleted, tomato mosaic virus (ToMV)-infected plant protoplasts contained an RNA-dependent RNA polymerase (RdRp) that utilized an endogenous template to synthesize ToMV-related positive-strand RNAs in a pattern similar to that observed in vivo. Despite the fact that only minor fractions of the ToMV 130- and 180-kDa replication proteins were associated with membranes, the RdR...

Japanese encephalitis virus (JEV) NS5 consists of an N-terminal guanylyltransferase/methyltransferase (MTase) domain and a C-terminal RNA-dependent RNA polymerase (RdRp) domain. We purified JEV NS5 from bacteria and examined its RdRp activity in vitro. It showed exclusive specificity for Mn(2+) and alkaline conditions (pH 8-10) for RdRp activity. It showed strong RdRp activity with dinucleotide...

The hepatitis C virus (HCV) genotype 2a isolate JFH1 represents the only cloned HCV wild-type sequence capable of efficient replication in cell culture as well as in vivo. Previous reports have pointed to NS5B, the viral RNA-dependent RNA polymerase (RdRp), as a major determinant for efficient replication of this isolate. To understand the contribution of the JFH1 NS5B gene at the molecular lev...

The recent outbreak of Zika virus (ZIKV) has imposed a serious threat to public health. Here we report the crystal structure of the ZIKV NS5 protein in complex with S-adenosyl-L-homocysteine, in which the tandem methyltransferase (MTase) and RNA-dependent RNA polymerase (RdRp) domains stack into one of the two alternative conformations of flavivirus NS5 proteins. The activity of this NS5 protei...

RNA-dependent RNA polymerases (RdRp) are very ancient enzymes and are essential for all viruses with RNA genomes. We reconstruct the origin and evolution of this polymerase since the initial stages of the origin of life. The origin of the RdRp was traced back from tRNA ancestors. At the origin of the RdRp the most ancient part of the protein is the cofactor-binding site that had the capacity of...