High molecular weight virion-associated RNA of vaccinia. A possible precursor to 8 to 12 S mRNA.

The high molecular weight virion-associated RNA synthesized by vaccinia in vitro can be cleaved into smaller components, some of which are extruded from the virus as 8 to 12 S RNA. The high molecular weight virion-associated RNA fails to bind appreciably (5%) to poly(U) filters indicating that it is not polyadenylated. Its cleavage products will, however, bind to poly(U) (40 to 50%) after processing in the presence of ATP. The high molecular weight virion-associated RNA is methylated by the virus, and purified unmethylated RNA can be methylated by detergent-solubilized extracts of vaccinia virus cores. In the presence of GTP, methylation is stimulated 3-fold. The level of methylation of purified unmethylated high molecular weight RNA achieved by soluble core extracts is approximately 80% of the level of methylation achieved with purified unmethylated 8 to 12 S viral RNA, suggesting that more residues than the primary 5' termini became methylated. Approximately 85% of the methylated RNA binds to poly(U) when purified high molecular weight RNA is processed with soluble core extracts in the presence of S-adenosyl[methyl-3H]methionine, GTP, and ATP, conditions which also cleave the RNA. Nucleic acid hybridization-competition studies indicate that virion-extruded 8 to 12 S mRNA contains sequences found in the high molecular weight virion-associated RNA.