IFNB1 and infection: With time, the levels of β-actin transcripts decreased equally in the two cell types and were significantly different (Mann–Whitney test, P<0.05) from those of mock-infected cells at 12 h post-infection (Fig. 6c); however, there was no difference in β-actin transcripts between PKR−/− and wt cells, indicating that the higher levels of IFN transcripts in wt cells resulted from specific enhancement of levels of IFN-β transcripts by PKR.