Maturation and degradation of ribosomal RNA in bacteria.

Ribosomal RNAs are the major components of ribosomes and are responsible for their catalytic activity. The three bacterial rRNAs (16S, 23S, and 5S) are cotranscribed as a single molecule that must be converted to the mature, functioning species through a series of nucleolytic processing events and base and sugar modifications that occur in the context of the assembling ribosome. One focus of this review is to examine the reactions that lead from the rRNA precursor to the mature species and to describe the ribonucleases (RNases) that carry out these processing reactions. rRNA, although usually stable in growing cells, also can be degraded if its assembly into ribosomes is aberrant or in response to certain stress conditions, such as starvation. The second focus of this review is to describe these degradative reactions, the RNases that carry them out, and the conditions that initiate the turnover process.