The influenza viral ribonucleoprotein complexes (vRNPs) are responsible for viral RNA synthesis. Each vRNP is comprised of one vRNA segment, the viral RNA dependent RNA polymerase complex (RdRP), and multiple copies of nucleoprotein (NP). NP serves as scaffold in formation of vRNPs, but also regulates vRNP activity. The N-terminus of NP contains a nonconventional nuclear localization signal (NLS1) essential for initial vRNP nuclear import, but also interacts with host RNA helicases to enhance viral RNA replication in the nucleus. NP contains at least one additional NLS sequence, with bioinformatics revealing a third NLS in some NP proteins.
Published yeast-two hybrid results indicate that the first 20 amino acids of NP can sufficiently bind with cellular protein UAP56. Suggesting the interaction of NP-UAP56 can be a major mechanism of how NP involve in viral replication. Thus, to examine the role of the N-terminus of NP aside from its vRNP nuclear localization activity N-terminal 20 amino acid deletion mutants with or without the addition of the conventional NLS from SV-40 T-antigen were constructed, termed del20NLS-NP and del20-NP. Nuclear localization of vRNPs with these constructs was assessed by GFP expression and western blotting. All these constructs exhibit nuclear localization, consistent with NLS1 being utilized for vRNP localization but not NP localization and vRNP formation in the nucleus. Furthermore, qPCR results demonstrated decreased vRNA synthesis activity, exacerbated as the vRNA template is lengthened in both plasmids, consistent with a lack of interaction with host RNA helicases. Interestingly, del20-NP vRNP activity is less severe than del20NLS-NP, suggesting perturbations of the N-terminus disrupt vRNP activity. To narrow down the region responsible for vRNA expression defect, del10-NP was constructed. GFP expression displayed similar activity between del10-NP and WT-NP with del20-NP showing a severe defection, suggesting NP amino acids 11-20 might be the major region responsible for the vRNA synthesis defect. However, sucrose density gradient results do not support the published interaction between NP and UAP56 in 293T cells. These results support the N-terminal region, potentially amino acids 11-20 of NP, is playing the important role in efficient viral gene expression during virus replication especially as vRNA template lengthen, and that the NLS1 of NP is not essential for NP/vRNP nuclear localization in our reconstituted vRNP assay.
| Identifer | oai:union.ndltd.org:csusb.edu/oai:scholarworks.lib.csusb.edu:etd-1760 |
| Date | 01 June 2018 |
| Creators | Lin, Jared |
| Publisher | CSUSB ScholarWorks |
| Source Sets | California State University San Bernardino |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses, Projects, and Dissertations |
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