Coordinated Regulation of 23S rRNA Maturation in Escherichia coli

In Escherichia coli, rRNAs are transcribed as precursors and require processing at the 3' and 5' ends to generate mature RNA molecules. The largest of these RNAs, 23S rRNA, is matured at the 3' end by a set of exonucleases and at the 5' end by an unknown RNase. Whether the 3' and 5' maturation steps occur independently or are coupled has previously been unclear. By assessing the levels of precursors accumulating at the 3' and 5' ends, we provide evidence that these processes may be linked. Thus, each of several conditions that led to precursor accumulation at one end also did so at the other end. We also observed that each end undergoes maturation at similar rates, suggesting that the two processes could be coupled. Finally, we provide evidence that processing at the 3' end facilitates 5'-end maturation. A model to explain the basis for the observed directionality of the reactions is proposed. This information will aid in the search for the enzyme responsible for final maturation of the 5' end of 23S rRNA.