ABSTRACT
The post-transcriptional processing of E. coli rRNA takes place in a defined series of steps (Fig. 1a). Following, and to some extent during, transcription of the 6000 nt primary transcript, the RNA folds up into a number of stem-loop structures by base pairing between complementary sequences in the transcript. The formation of this secondary structure of stems and loops allows some proteins to bind to form a ribonucleoprotein (RNP) complex. Many of these proteins remain attached to the RNA and become part of the ribosome. After the binding of proteins, modifications such as 24 specific base methylations take place. S-Adenosylmethionine (SAM) is the methylating agent, and usually a methyl group is added to the base adenine. Primary cleavage events then take place, mainly carried out by RNase III, to release precursors of the 5S, 16S and 23S molecules. Further cleavages at the 5- and 3-ends of each of these precursors by RNases M5, M16 and M23, respectively, release the mature length rRNA molecules in a secondary cleavage step.
