FIG. 2.

Single-round transcription in vitro with limiting amounts of RNA polymerase. Conditions are as described in the legend to Fig. 1A, except that 10 nM RNA polymerase was used instead of 100 nM to transcribe the wild-type and the indicated mutant promoters. (A) Section of the gel corresponding to the control P_sp promoter, giving rise to a 488-nucleotide mRNA, and the wild-type P_ttgG or its single-point mutation derivative. (B) Relative levels of transcripts from P_ttgG. We assigned a relative value of 1 to the amount made from the wild type.