Expression of early genes of origin-defective mutants of simian virus 40

The nucleotide sequences of eight origin-defective mutants of simian virus 40 have been determined. All of the mutants have suffered deletions, which range in size from 4 to 241 nucleotides. Some of the mutants induce the synthesis of tumor (T) antigen, others do not. Viral mRNA extracted from rat cells transformed by two of the T-antigen-positive mutants has been analyzed by the S1 nuclease technique of Berk and Sharp. Irrespective of the size or the location of the deletions, the 5' ends of viral mRNAs are located approximately the same distance from the A+T-rich region (A-T-T-T-A-T) rather than at a specific site in the viral genome.