FIG. 6.

Primer extension assay for NA-specific cRNA and mRNA. (A) NA-specific cRNA and mRNA levels in cells infected with the A₆ mutant (A₆) and the wild-type virus (WT). Total RNA from infected cells was isolated at the indicated time points p.i. The expected products for NA cRNA (142 nt), NA mRNA (152 to 157 nt), HA cRNA (94 nt), and HA mRNA (104 to 109 nt) are indicated. Since influenza virus mRNAs are initiated by capped RNA primers, which are heterogeneous in size, primer extension products of the mRNA are expected to produce a broad band which is 10 to 15 nt longer than that produced by products of cRNA. (B) NA cRNA-to-HA cRNA ratios in cells infected with the A₆ mutant or the wild-type virus. (C) NA mRNA-to-HA mRNA ratio in cells infected the A₆ mutant or the wild-type virus.