International audienceRNAs can be either transcribed directly as functional species or as molecules that require post-transcriptional processing by ribonucleases. Most messenger RNAs fall into the first category, while most structural RNAs fall into the second. There are, however, some specific examples of mRNAs that undergo processing to shorter, more stable species with a higher translational yield. Most of the work in this field has been performed in E. coli and, more recently, in B. subtilis. In this chapter, I will first describe some examples of mRNA processing these two organisms and then compare their pathways of stable RNA maturation. While there is some degree of overlap between their RNA processing enzymes and pathways, for the most part they are remarkably different, far more divergent than was ever predicted before the sequencing of their respective genomes. None of the late steps in rRNA maturation are conserved between the two bacteria, for example. In addition, B. subtilis utilizes an enzyme with 5β exoribonuclease activity for mRNA and rRNA processing, whereas E. coli does not appear to possess a 5β exoribonuclease. These observations highlight the importance of studying more than one model bacterial system in fine detail
