Fluorescent primer extension analysis of transcriptional start sites for the preAB and ygiW -STM3175 operons. Electropherograms of the labeled cDNA are shown for preA (A) and ygiW (C). Dashed lines mark the relative fluorescence unit (RFU) cut-off, below which does not give a confident signal strength. Asterisks (*) denote which cDNA peak was analyzed. Labeled cDNA electropherograms (filled peaks) were aligned with sequence chromatograms (open peaks) to identify the base at which transcription starts for both preAB (B) and ygiW-STM3175 (D). Results of transcriptional organization are diagramed as shown with start sites mapped relative to the translational start (E). PreA appears to activate transcription of each of the three operons defined in the preA region (dashed lines denote positive regulation).