Simian virus 40 cRNA is processed into functional mRNA in microinjected monkey cells.

Monkey cells, microinjected with simian virus 40 (SV40) in vitro synthesized cRNA produce full-size tumor (T)-antigen. This was verified by analyzing immunoprecipitates of microinjected cells by polyacrylamide gel electrophoresis. Early SV40 DNA contains an intron within the large T-antigen coding sequences. Therefore, cRNA copied in vitro from the early DNA strand requires removal of the intron in order to become a functional mRNA. Polyadenylation of the cRNA in vitro by Escherichia coli poly(A)-polymerase increased the biological activity of the RNA. Detection of T-antigen by gel electrophoresis required as little as 50 poly(A)-cRNA injected cells. Splicing of the microinjected cRNA appears to be a nuclear process. Cells enucleated by cytochalasin B prior to injection do not synthesize large T-antigen. However, small t-antigen, a protein with a continuous sequence, is synthesized in these cells. Finally, it is shown that the process of splicing is not required for the transport of mRNA from the nucleus into the cytoplasm. Authentic T-antigen mRNA, isolated from virus infected cells, induced T-antigen synthesis with similar efficiency after either nuclear or cytoplasmic injection.