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

Abstract

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 [ 3 H]methionine or 32 P 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 (m 7 GpppX m p Yp), and the latter is probably a cap 0 (m 7 GpppXp). On the basis of relative labeling of the two caps with [ 3 H]adenosine and [ 3 H]guanosine, we concluded that each cap contained at least one adenosine residue in addition to guanosine and, therefore, that cap 0 contained m 7 GpppAp. Cleavage of [ 3 H]methionine-labeled viral RNA with tobacco acid pyrophosphatase released a labeled component that cochromatographed on polyethyleneimine-cellulose with m 7 Gp, confirming the m 7 GpppX 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 32 P 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.