MEF/wt cells (A) or MEF/PKR0/0 cells (B) were mock-infected or infected with MP-12, rMP12-C13type, rMP12-NSsR173A, or rMP12-mPKRN167 at an moi of 1.0 or 0.01, and culture supernatants were collected at 16 hpi or 72 hpi, respectively, to determine the viral titer by plaque assay of VeroE6 cells. (C) MRC-5 cells were infected with MP-12, rMP12-C13type or rMP12-NSsR173A at moi of 3.0 or 0.01, and virus titer at 16 hpi or 72 hpi were measured, respectively. Mean +/− standard deviations of three independent experiments are shown in the graph. Unpaired Student’s t-test was performed to compare to the value of MP-12: **p<0.01, *p<0.05.