FIG. 6.

NA-specific mRNA and cRNA levels in cells infected with transfectant D2 or D1/2. Total RNAs from MDBK cells infected at an MOI of 2 with wild-type (WT) A/WSN/33 virus or the D2 or D1/2 transfectant were extracted at the indicated time points postinfection (p.i.) and subjected to primer extension analysis, using primers specific for the positive-sense NA and HA RNAs. Primer extension products were analyzed on a 5% polyacrylamide gel containing 7 M urea. The expected length of the primer extension products for the NA cRNA is 125 nt; that for the NA mRNA is about 135 to 140 nt due to the presence of host cell mRNA-derived heterogeneous capped RNA primers at the 5′ end of viral mRNAs. The expected length of HA-specific extension products is 94 nt for the cRNA and about 104 to 109 nt for the mRNA. Size markers in nucleotides are shown on the left.