Arnold Berk

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 approximately 0.67 to approximately 0.60 and from approximately 0.54 to approximately 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 approximately 0.67 to approximately 0.54 and from approximately 0.54 to approximately 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 approximately 0.67 and approximately 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.