Identification of a promoter component involved in positioning the 5' termini of simian virus 40 early mRNAs.

The 5' termini of the principal early mRNAs produced in cells transformed by wild-type simian virus 40 lie 21-25 nucleotides downstream from an A-T-T-T-A-T sequence on the DNA template. The 5' termini of early mRNAs produced by five origin-defective mutants containing deletions downstream from the A-T-T-T-A-T sequence and one viable mutant dl892 with a deletion starting 15 nucleotides upstream from this sequence were determined by a method involving synthesis, separation, and determination of the sequences of DNAs complementary to 5' termini. Mutant dl892 produced early mRNAs with the same principal 5' termini as wild-type virus; the origin-defective mutants produced mRNAs with principal 5' termini shifted downstream by a distance equivalent to the length of the deleted DNA segment. These data suggest that a DNA sequence of 29 nucleotides, which includes the A-T-T-T-A-T sequence, contains a component(s) of a promoter for early transcription. This component functions in positioning the 5' ends of the principal early mRNAs 21-25 nucleotides downstream from the A-T-T-T-A-T sequence and acts independently of these downstream sequences.