Capping of Viral RNA in Cultured Spodoptera frugiperda Cells Infected with Autographa californica Nuclear Polyhedrosis Virus

Viral RNA from fall armyworm (Spodoptera frugiperda) cells infected with Autographa californica nuclear polyhedrosis virus contains cap structures. Most of the cap labeled in vivo with [³H]methionine or ³²P_i cochromatographed on DEAE-cellulose with the −5 charge marker; a minor component appeared at −4 net charge. The former is probably a cap 1 structure (m⁷GpppX^m_pYp), and the latter is probably a cap 0 (m⁷GpppXp). On the basis of relative labeling of the two caps with [³H]adenosine and [³H]guanosine, we concluded that each cap contained at least one adenosine residue in addition to guanosine and, therefore, that cap 0 contained m⁷GpppAp. Cleavage of [³H]methionine-labeled viral RNA with tobacco acid pyrophosphatase released a labeled component that cochromatographed on polyethyleneimine-cellulose with m⁷Gp, confirming the m⁷GpppX linkage in the cap. These results were also seen with host polyadenylated RNA. The caps appeared in nearly equal abundance in viral polyadenylated and non-polyadenylated RNAs. The ratio of ³²P_i incorporated into the cap to that incorporated into mononucleotides suggested average lengths for the polyadenylated and non-polyadenylated RNAs of 1,800 and 1,200 nucleotides, respectively.