Promoter mutations in the transfer RNA gene tyrT of Escherichia coli

The DNA sequences for nine independent promoter mutants of a tyrosine tRNA gene, tyrT of Escherichia coli, are reported. The nine mutations involve six transitions, two transversions, and one deletion. They are located at four different sites in the first 30 base pairs preceding the start point of transcription. The changes found are: a T.A to A.T transversion at position -8 (two mutants); a T.A to C.G transition at position -8 (three mutants); a T.A to C.G transition at position -13 (two mutants); a T.A to C.G transition at position -16 (one mutant); and a deletion of a G.C base pair at position -26/27 (one mutant). Four of the five different mutant tyrT promoters have alterations at positions that might have been expected from DNA sequence studies with other prokaryote promoters. One of these mutants (a G.C deletion at position -26/27) occurs in a stretch of eight consecutive G.C base pairs which may be characteristic of stable RNA promoters.