Fig. 1: The viral RNA genome stabilizes the intrinsically disordered protein SARS-CoV-2 N to allow formation of filamentous structures.
A Schematic diagram of full-length Hu-1 SARS-CoV-2 N and truncation mutants. IDRNTD, intrinsically disordered region located at the NTD; RNA-BD, RNA-binding domain; IDRcentral, intrinsically disordered region connecting the rigid domains RNA-BD and DD; DD, dimerization domain; IDRCTD, intrinsically disordered region located at the CTD. The mutations in BA.1. (Omicron) strains are indicated (BA.1. N). B Specific melting temperatures calculated by Differential Scanning Calorimetry of the constructs shown in A and the type of model used for data processing are indicated. C DSC thermograms of the constructs shown in B. Source data are provided as a Source Data file. D Size exclusion chromatogram of SARS-CoV-2 N (left panel, black). The theoretical mass of the N monomer is 48.6 kDa for reference. The inset shows SDS-PAGE gel analysis of pure SARS-CoV-2 N, along with molecular mass markers (in kDa) for standard proteins. The SEC-MALS chromatogram (right panel, red) shows a molecular weight of ~94 kDa. Native Mass-Spectrometry (Native MS) analysis of the purified sample shows a majority of RNA-free N dimer in the samples. The specific MWs are indicated in the inset table. A representative micrograph of three independent experiments of negative staining electron microscopy (NS-EM) of the flexible dimer is shown (scale bar 100 nm). E Combination of purified SARS-CoV-2 N and purified viral genome of natural SARS-CoV-2 strain virions. Created in BioRender. Saphire, E. (2025) https://BioRender.com/eqzcpd4. Three representative micrographs of three independent experiments of NS-EM showing straight and curved filamentous structures are shown (scale bar 100 nm). 2D averaged classes of these filaments (ovals on right) similar to those found in native capsids of Murine CoVs26 (Supplementary Fig. 1).
