FIG. 3.

Effects of mutations in the PA subunit on RNA synthesis in vivo. 293T cells were transfected with plasmids expressing vRNA-like CAT RNA reporter, NP, PB1, PB2, and either a wild-type (WT) PA or mutant PAs. Cell extracts were tested for polymerase activity 24 h posttransfection by measuring the levels of vRNA, mRNA, and cRNA by primer extension. Sizes are indicated, in nucleotides, on the left. Positions of vRNA, mRNA, and cRNA signals are indicated on the right. The extension product of the 5S rRNA, with an expected size of 62 nt, is indicated on the right as an internal control.