Analysis of rnr transcriptional unit. (a) Schematic representation of the rnr transcriptional unit showing the secG promoter (PsecG) identified in this work. The arrows indicate the approximate location and orientation (sense/antisense) of some primers used in RT-PCR, primer extension and RACE experiments. (b) secG, rnr and smpB are co-transcribed. The transcripts were detected by RT-PCR performed with 100 ng of total RNA extracted from the wild type strain at 15°C or 37°C as indicated on top of the lanes. Forward primers annealed to the upstream gene and reverse primers to the downstream gene. Parallel RT-PCR reactions run in the absence of reverse transcriptase yielded no product. RT-PCR with primers specific for 16S rRNA shows that there were not significant variations in the amount of RNA used in each sample.