Biochemical methods are presented for determining the structure of spliced RNAs present in cells at low concentrations. Two cytoplasmic spliced viral RNAs were detected in CV-1 cells during the early phase of simian virus 40 (SV40) infection. One is 2200 nucleotides in length and is composed of two parts, 330 and 1900 nucleotides, mapping from ∼0.67 to ∼0.60 and from ∼0.54 to ∼0.14, respectively, on the standard viral map. The other is 2500 nucleotides long and also is composed of two parts, 630 and 1900 nucleotides mapping from ∼0.67 to ∼0.54 and from ∼0.54 to ∼0.14, respectively. Correlation of the structure of these mRNAs with the structure of the early SV40 proteins, small T antigen (17,000 daltons) and large T antigen (90,000 daltons), determined by others suggests that: ( i ) translation of the 2500-nucleotide mRNA yields small T antigen; ( ii ) translation of the 2200-nucleotide mRNA proceeds through the splice point in the RNA to produce large T antigen (and thus large T antigen is encoded in two separate regions of the viral genome); and ( iii ) the DNA sequences between ∼0.67 and ∼0.60 present in both mRNAs are translated in the same reading frame in both mRNAs to yield two separate gene products that have the same NH 2 -terminal sequence. Therefore, expression of the early SV40 genes is partially controlled at the level of splicing of RNAs.

Berk, A. J., & Sharp, P. A. (1978). Spliced early mRNAs of simian virus 40. Proceedings of the National Academy of Sciences, 75(3), 1274–1278.