Figure 1. SARS-CoV-2 nsp13 helicase forms a stable complex with the holo-RdRp and an RNA scaffold.
a. RNA scaffold used for biochemistry, native mass spectrometry (nMS), and cryo-EM.
b. Native gel electrophoretic mobility shift assay reveals that nsp13 forms a stable complex with holo-RdRp:RNA. The 4.5% polyacrylamide gel was visualized with Gel Red to stain the RNA.
c. nMS spectra and the corresponding deconvolved spectra for the holo-RdRp containing the RNA scaffold (a) with and without nsp13. The measured mass for the holo-RdRp:RNA complex corroborates the established stoichiometry of 1:2:1:1 for nsp7:nsp8:nsp12:RNA (Hillen et al., 2020; Kirchdoerfer and Ward, 2019; Wang et al., 2020; Yin et al., 2020), respectively (bottom). Addition of the 67.5-kDa nsp13 helicase to the RNA-bound holo-RdRp holo sample forms a transcription complex/helicase assembly with 1:1 stoichiometry (top).