Mutational analysis of Influenza B NS1 protein. (a). Sequence alignment (between amino acids 81 and 102) of Lee-NS1 and the mutants Lee-NS1 D92N, Lee-NS1 D92A, Lee-NS1 M91A, Lee-NS1 P93A and Lee-NS1 S94P. Also shown are 117-NS1 and 117-NS1 P94S. (B–E). Protein expression profile of (b) Lee-NS1 wild-type (WT) and mutant Lee-NS1 D92A, (c). 132-NS1 wild-type (WT), 132-NS1 N92D, Lee-NS1 wild-type (WT) and Lee-NS1 D92N, (d). Lee-NS1 wild-type (WT), Lee-NS1 M91A, Lee-NS1 P93A, Lee-NS1 S94P and (e). 117-NS1 wild-type (WT) and 117-NS1 P94S. At 16 h post transfection, NS1 protein was detected by immunoblotting with anti-FLAG. pC: Cells transfected with empty pCAGGS vector. Protein bands corresponding to NS1-FLAG (black arrow) and p23-FLAG (*) are indicated.