Methylation of nuclear simian virus 40 RNAs.

Nuclear RNAs, pulse-labeled with [methyl-3H]methionine and [3H]uridine under optimal conditions, were prepared from cells infected with simian virus 40 at a late time after infection. The labeled RNAs were hybridized with restriction fragments of simian virus 40 DNA. Levels of methyl-3H-labeled RNA annealing with the early (E) or late (L) strands of a particular restriction fragment were compared with [3H]uridine-labeled RNA annealing with the same fragment. The methyl-3H-labeled RNA hybridizing to the various restriction fragments was eluted and analyzed for caps and internal 6-methyladenosine residues. Caps of transcripts of both the L and E strands were primarily located in a fragment containing the origin for viral DNA replication. The highest level of the internal 6-methyladenosine residues in simian virus 40 nuclear RNA was located on the L strand within a fragment from 83 to 0.0 map units and in RNA transcripts from the E strand within a fragment from 37 to 67 map units. Portions of both these regions represent intervening sequences not represented in cyotplasmic mRNA's. Lower levels of internal methylation were found in other locations as well. The potential role of internal 6-methyladenosine residues in RNA processing and transport from the nucleus to the cytoplasm is discussed.