Fig 1: Nsp1 N-terminal and central domain mutants are defective for ribosome and mRNA binding(A) HEK293T cells were transfected with plasmids expressing WT or the indicated mutant 3xFLAG-Halo-tagged nsp1. Nsp1 was immunoprecipitated (IP) using ?-FLAG beads and coIP of ribosomal proteins RACK1, RPS2, RPS3, and RPS24 was monitored by western blotting, with vinculin serving as a loading control. Input lanes contain 1/10 of the amount of protein used for the IPs.(B) Equilibrium binding measurements of fluorescently labeled WT (blue), R124A,K125A (red), and R99A (green) nsp1 to purified ribosomes. Data represent a total of 3 biological replicates.(C) HEK293T cells were co-transfected with HBB-nLuc and either a control plasmid or the indicated 3xFLAG-Halo-tagged nsp1 constructs. Technical triplicate measurements were taken for each biological replicate. A total of at least three biological replicates were taken for each measurement. Nsp1 was immunoprecipitated using ?-FLAG beads, whereupon the co-immunoprecipitating RNAs were extracted and nLuc mRNA was quantified by qRT-PCR. The mRNA values were then normalized to the values obtained from the empty vector control. Each dot represents an independent experiment. *p = 0.05, **p = 0.01; one-way ANOVA followed by Dunnett’s multiple comparisons test versus WT nsp1. The bars represent the mean value of the replicates and error bars represent standard deviation.(D) HEK293T cells were co-transfected with a 3xFLAG-Halo-tagged nsp1 plasmid or empty vector control, together with a plasmid expressing either GFP with a 5' stem loop (GFP+SL) or a control GFP lacking the stem loop (GFP). Nsp1 was immunoprecipitated using ?-FLAG beads, whereupon the co-immunoprecipitating GFP+SL or GFP mRNAs were quantified by qRT-PCR. The mRNA values were then normalized to those obtained from the empty vector control. The bars represent the mean value of the replicates and error bars represent standard deviation.(E) The levels of GFP+SL and GFP mRNA present in the input samples from (D) were quantified by qRT-PCR and normalized to 18S rRNA, with the level of GFP mRNA in cells lacking nsp1 (empty vector control) set to 1. Each dot represents an independent experiment. **p = 0.01; unpaired t test. See also Figures S4, S5, and S6. The bars represent the mean value of the replicates and error bars represent standard deviation.