Affiliation:
1. Institut für Virologie, The Calicilab, Medizinische Fakultät Carl Gustav Carus, Fiedlerstrasse 42, D-01307 Dresden, Germany
Abstract
ABSTRACT
Noroviruses (
Caliciviridae
) are RNA viruses with a single-stranded, positive-oriented polyadenylated genome. To date, little is known about the replication strategy of norovirus, a so-far noncultivable virus. We have examined the initiation of replication of the norovirus genome in vitro, using the active norovirus RNA-dependent RNA polymerase (3D
pol
), homopolymeric templates, and synthetic subgenomic or antisubgenomic RNA. Initiation of RNA synthesis on homopolymeric templates as well as replication of subgenomic polyadenylated RNA was strictly primer dependent. In this context and as observed for other enteric RNA viruses, i.e., poliovirus, a protein-primed initiation of RNA synthesis after elongation of the VPg by norovirus 3D
pol
was postulated. To address this question, norovirus VPg was expressed in
Escherichia coli
and purified. Incubation of VPg with norovirus 3D
pol
generated VPg-poly(U), which primed the replication of subgenomic polyadenylated RNA. In contrast, replication of antisubgenomic RNA was not primer dependent, nor did it depend on a leader sequence, as evidenced by deletion analysis of the 3′ termini of subgenomic and antisubgenomic RNA. On nonpolyadenylated RNA, i.e., antisubgenomic RNA, norovirus 3D
pol
initiated RNA synthesis de novo and terminated RNA synthesis by a poly(C) stretch. Interestingly, on poly(C) RNA templates, norovirus 3D
pol
initiated RNA synthesis de novo in the presence of high concentrations of GTP. We propose a novel model for initiation of replication of the norovirus genome by 3D
pol
, with a VPg-protein-primed initiation of replication of polyadenylated genomic RNA and a de novo initiation of replication of antigenomic RNA.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology
Cited by
76 articles.
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