MxB stalk mutants and antiviral activity. (A) The MxB protein schematic highlights regions of sequence diversity from the human MxA protein; each red dot denotes an MxB position where 5 consecutive residues differed from MxA. (B) Antiviral activities of MxB stalk mutant proteins. Results are an average of at least 5 independent experiments, with error bars denoting 95% confidence intervals. (C) Representative immunofluorescent microscopy results; white bar, 10 μm. See Additional file 4: Figure S4 for results of quantitative western blotting.