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 [3H]methionine or 32pI cochromatographed on DEAE-cellulose with the-5 charge marker; a minor com onent appeared at-4 net charge. The former is probably a cap 1 structure (m GpppXmYp), and the latter is probably a cap 0 (m7GpppXp). On the basis of relative labeling of the two caps with [3H]adenosine and [ H]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 nonpolyadenylated RNAs. The ratio of 32p; 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. Since the cap structure was first identified by Furuichi (7) at the 5' terminus of mRNA from cytoplasmic polyhedrosis virus, caps have been reported in most eucaryotic mRNAs. RNAs from certain animal (2, 6) and plant (4) viruses and lower eucaryotes (5, 20) contain a cap 0 structure (m7GpppXp) (19). Other viral mRNAs (8, 22) and mRNAs from higher eucaryotes contain a cap 1 with one additional methyl group (m7GpppXpYp) (1). Mammalian mRNAs have a minor amount of a further methylated cap species, cap 2 (m7GpppXmY'Zp) (3). These cap species all resist hydrolysis by alkali or RNase T2 because of the unusual 5'-5' triphosphate linkage and the 2'-O-methylation on the X and Y residues that prevents formation of the 2',3'

Mapping of Early and Late Transcripts Encoded by the Autographa californica Nuclear Polyhedrosis Virus Genome: Is Viral RNA Spliced?

“…Cytoplasmic RNA from AcNPV-infected S. fiigiper-dai cells was isolated at 18 h postinfection and total cellular RNA at 24 h postinfection. The possibility existed that some mRNAs did not carry poly(A) residues (14). Fragment sizes are given in base pairs.…”