title: Hepatitis C virus nonstructural protein 5A (NS5A) is an RNA-binding protein.
abstract: Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) has been shown to antagonize numerous cellular pathways, including the antiviral interferon-alpha response. However, the capacity of this protein to interact with the viral polymerase suggests a more direct role for NS5A in genome replication. In this study, we employed two bacterially expressed, soluble derivatives of NS5A to probe for novel functions of this protein. We find that NS5A has the capacity to bind to the 3'-ends of HCV plus and minus strand RNAs. The high affinity binding site for NS5A in the 3'-end of plus strand RNA maps to the polypyrimidine tract, an element known to be essential for genome replication and infectivity. NS5A has a preference for single-stranded RNA containing stretches of uridine or guanosine. Values for the equilibrium dissociation constants for high affinity binding sites were in the 10 nM range. Two-dimensional gel electrophoresis followed by Western blotting revealed the presence of unphosphorylated NS5A in Huh-7 cells stably expressing the subgenomic replicon. Moreover, RNA immunoprecipitation and NS5A pull-down experiments showed the capacity of replicon-derived NS5A to bind to synthetic RNA and the HCV genome, respectively. Deletion of all of the casein kinase II phosphorylation sites in NS5A supported stable replication of a subgenomic replicon in Huh-7. However, this derivative could not be labeled with inorganic phosphate, suggesting that extensive phosphorylation of NS5A is not required for the replication functions of NS5A. The discovery that NS5A is an RNA-binding protein defines a new functional target for development of agents to treat HCV infection and a new structural class of RNA-binding proteins.
authors.affiliation: Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Luyun
authors.initials: L
authors.lastname: Huang
authors.forename: Jungwook
authors.initials: J
authors.lastname: Hwang
authors.forename: Suresh D
authors.initials: SD
authors.lastname: Sharma
authors.forename: Michele R S
authors.initials: MR
authors.lastname: Hargittai
authors.forename: Yingfeng
authors.initials: Y
authors.lastname: Chen
authors.forename: Jamie J
authors.initials: JJ
authors.lastname: Arnold
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Raney
authors.forename: Craig E
authors.initials: CE
authors.lastname: Cameron
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D019921:Biotinylation; D015153:Blotting, Western; D003101:Collodion / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D016679:Genome, Viral; D006157:Guanosine Monophosphate / Q000737:chemistry; D047468:Immunoprecipitation; D007700:Kinetics; D008957:Models, Genetic; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011743:Pyrimidines / Q000737:chemistry; D012313:RNA / Q000737:chemistry; D016601:RNA-Binding Proteins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D014158:Transcription, Genetic; D014466:Ultraviolet Rays; D014542:Uridine Monophosphate / Q000737:chemistry; D017361:Viral Nonstructural Proteins / Q000378:metabolism / Q000502:physiology*; D012324:RNA-Dependent RNA Polymerase
chemical_list: D003101:Collodion; D003432:Cross-Linking Reagents; D006157:Guanosine Monophosphate; D009841:Oligonucleotides; D011743:Pyrimidines; D012313:RNA; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D014542:Uridine Monophosphate; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase