Maturation of the 3' end of 5-S ribosomal RNA from Escherichia coli

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.

An Archaea 5S rRNA analog is stably expressed in Escherichia coli

Mini-genes for 5S-like rRNA were constructed. These genes had a sequence which largely resembles that of the naturally occurring 5S rRNA of a bacterium, Halococcus morrhuae, which phylogenetically belongs to the Archaea. Plasmids carrying the mini-genes were transformed into Escherichia coli (Ec). Ribosomal incorporation was not a prerequisite for stable accumulation of the RNA product. However, only those constructs with a well-base-paired helix I accumulated RNA product. This result strongly implies that this aspect of the structure is likely to be an important condition for stabilizing 5S rRNA-like products. The results are consistent with our current understanding of 5S rRNA processing in Ec. When used in conjunction with rRNA probe technology, the resulting chimeric RNA may be useful as a monitoring tool for genetically engineered microorganisms or naturally occurring organisms that are released into the environment.

RNA processing in prokaryotic cells

RNA processing in Escherichia coli and some of its phages is reviewed here, with primary emphasis on rRNA and tRNA processing. Three enzymes, RNase III, RNase E and RNase P are responsible for most of the primary endonucleolytic RNA processing events. The first two are proteins, while RNase P is a ribozyme. These three enzymes have unique functions and in their absence, the cleavage events they catalyze are not performed. On the other hand a relatively large number of exonucleases participate in the trimming of the 3' ends of tRNA precursor molecules and they can substitute for each other. Primary processing is the first event that happens to the nascent RNA molecule, while in secondary RNA processing, the substrate is a product of a primary processing event. Although most RNA processing occurs in RNP particles, it seems that only in secondary RNA processing is the RNP particle required for the reaction. Bacteria and especially bacteriophages contain self-splicing introns which in cases were probably acquired from other species.