Regulation of the Escherichia coli rrnB P2 promoter

The seven rRNA operons in Escherichia coli each contain two promoters, rrn P1 and rrn P2. Most previous studies have focused on the rrn P1 promoters. Here we report a systematic analysis of the activity and regulation of the rrnB P2 promoter in order to define the intrinsic properties of rrn P2 promoters and to understand better their contributions to rRNA synthesis when they are in their natural setting downstream of rrn P1 promoters. In contrast to the conclusions reached in some previous studies, we find that rrnB P2 is regulated: it displays clear responses to amino acid availability (stringent control), rRNA gene dose (feedback control), and changes in growth rate (growth rate-dependent control). Stringent control of rrnB P2 requires the alarmone ppGpp, but growth rate-dependent control of rrnB P2 does not require ppGpp. The rrnB P2 core promoter sequence (-37 to +7) is sufficient to serve as the target for growth rate-dependent regulation.     

Sequence and characterisation of a ribosomal RNA operon fromAgrobacterium vitis

One of the four ribosomal RNA operons (rrnA) from theAgrobacterium vitis vitopine strain S4 was sequenced.rrnA is most closely related to therrn operons ofBradyrhizobium japonicum andRhodobacter sphaeroides and carries an fMet-tRNA gene downstream of its 5S gene, as in the case ofR. sphaeroides. The 16S rRNA sequence of S4 differs from theA. vitis K309 type strain sequence by only one nucleotide, in spite of the fact that S4 and K309 have very different Ti plasmids. The predicted secondary structure of the S4 23S rRNA shows several features that are specific for the alpha proteobacteria, and an unusual branched structure in the universal B8 stem. The 3′ ends of the three otherrrn copies of S4 were also cloned and sequenced. Sequence comparison delimits the 3′ ends of the four repeats and defines two groups:rrnA/rrnB andrrnC/rrnD.