ABSTRACT
Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging bunyavirus that causes novel zoonotic diseases in Asian countries including China, Japan, South Korea, and Vietnam. In phleboviruses, viral proteins play a critical role in viral particle formation inside the host cells. Viral glycoproteins (GPs) and RNA-dependent RNA polymerase (RdRp) are colocalized in the Golgi apparatus and endoplasmic reticulum-Golgi intermediate compartment (ERGIC). The nucleocapsid (N) protein was widely expressed in the cytoplasm, even in cells coexpressing GP. However, the role of SFTSV N protein remains unclear. The subcellular localization of SFTSV structural proteins was investigated using a confocal microscope. Subsequently, minigenome and immunoprecipitation assays were carried out. The N protein interacts with viral RNA (vRNA) and further shows translational activity with RdRp which is L protein and localized in the ERGIC and Golgi apparatus when co-expressed with GP. On the other hand, mutant N protein did not interact with vRNA either localized in the ERGIC or Golgi apparatus. The interaction between the N protein of SFTSV and vRNA is important for the localization of viral proteins and viral assembly. This study provides useful insights into the life cycle of SFTSV, which will lead to the detection of antiviral targets.
Subject(s)
Endoplasmic Reticulum/metabolism , Golgi Apparatus/metabolism , Nucleocapsid Proteins/metabolism , RNA, Viral/metabolism , RNA-Dependent RNA Polymerase/metabolism , Ribonucleoproteins/metabolism , Severe Fever with Thrombocytopenia Syndrome/metabolism , Viral Envelope Proteins/metabolism , Animals , Chlorocebus aethiops , HEK293 Cells , Humans , Nucleocapsid Proteins/genetics , RNA-Dependent RNA Polymerase/genetics , Ribonucleoproteins/genetics , Vero Cells , Viral Envelope Proteins/geneticsABSTRACT
Severe fever with thrombocytopenia syndrome virus subclone B7 shows strong plaque formation and cytopathic effect induction compared with other subclones and the parental strain YG1. Compared to YG1 and the other subclones, only B7 possesses a single substitution in the L protein at the amino acid position 1891, in which N is changed to K (N1891K). In this study, we evaluate the effects of this mutation on L protein activity via a cell-based minigenome assay. Substitutions of N with basic amino acids (K or R) enhanced polymerase activity, while substitutions with an acidic amino acid (E) decreased this activity. Mutation to other neutral amino acids showed no significant effect on activity. These results suggest that the characteristic of the amino acid at position 1891 of the L protein are critical for its function, especially with respect to the charge status. Our data indicate that this C-terminal domain of the L protein may be crucial to its functions in genome transcription and viral replication.
