Fig. 6. The function of 3′ vRNA as template for the initiation of viral mRNA synthesis requires the formation of three base-pairs with 5′ vRNA. (A) The sequence of bases 11–16 and bases 10–15 in 5′ and 3′ vRNA oligonucleotides, respectively, used to assess the role of hydrogen bond formation between 5′ and 3′ vRNA. (B) ³²P-labeled capped CA-containing RNA was incubated with the nuclear extract in the presence of the four NTPs and the indicated 5′ and 3′ RNA pairs denoted in (A). (C) Base-pairing between 5′ and 3′ vRNA during the initiation of mRNA synthesis. Solid lines denote base-pairs required for initiation; dotted lines indicate base-pairs that enhance initiation.