FIG. 7.

Transcription from wild-type and mutant codBA promoters. (A) Sequence of the wild-type codBA promoter region with the −10 region underlined and the G7 and A8 start sites labeled with the number 7 or 8, respectively. Horizontal arrows indicate transcription initiation at the two start sites. The two T-to-G substitutions that created the TGTG mutant promoter are shown in gray. (B) Levels of codB::lacZ transcripts initiated at the wild-type and TGTG mutant promoters. Cells carrying either the wild-type or TGTG mutant codB::lacZ fusion were grown under conditions of pyrimidine excess or limitation, and fusion transcript levels were measured by quantitative primer extension mapping (137). Transcript levels are in arbitrary units. (Modified from reference 137 with permission from Elsevier.)