FIG. 4.

Secondary structure of the 5′ untranslated region of the sol operon transcript and effect of targeted mutations on transcription start mapping by primer extension. (A) Secondary structure of the beginning of the sol operon transcript, as determined by the program MFold and plotted by the program PlotFold. The positions of the second primer extension signal, which led to deduction of P₂, and the region used for targeted mutagenesis are indicated. RBS, ribosome-binding site. (B) Primer extension experiments showing signals related to P₁ (distal promoter) and P₂ (proximal start site). The results of sequence reactions, which were obtained by using the same oligodeoxynucleotides, are shown on the left in each gel. mut, mutated region; nat, natural sequence.