Degradosome

The degradosome is a multiprotein complex present in most bacteria that is involved in the processing of ribosomal RNA and the degradation of messenger RNA and is regulated by Non-coding RNA. It contains the proteins RNA helicase B, RNase E and Polynucleotide phosphorylase. The degradosome is a multiprotein complex present in most bacteria that is involved in the processing of ribosomal RNA and the degradation of messenger RNA and is regulated by Non-coding RNA. It contains the proteins RNA helicase B, RNase E and Polynucleotide phosphorylase. The store of cellular RNA in the cells is constantly fluctuating. For example, in Escherichia coli, Messenger RNA's life expectancy is between 2 and 25 minutes, in other bacteria it might last longer. Even in resting cells, RNA is degraded in a steady state, and the nucleotide products of this process are later reused for fresh rounds of nucleic acid synthesis. RNA turnover is very important for gene regulation and quality control. All organisms have various tools for RNA degradation, for instance ribonucleases, helicases, 3'-end nucleotidyltransferases (which add tails to transcripts), 5'-end capping and decapping enzymes and assorted RNA-binding proteins that help to model RNA for presentation as substrate or for recognition. Frequently, these proteins associate into stable complexes in which their activities are coordinate or cooperative. Many of these RNA metabolism proteins are represented in the components of the multi-enzyme RNA degradosome of Escherichia coli, which is constituted by four basic components: the hydrolytic endo-ribonuclease RNase E, the phosphorolytic exo-ribonuclease PNPase, the ATP-dependent RNA helicase (RhIB) and a glycolytic enzyme enolase. The RNA degradosome was discovered in two different laboratories while they were working on the purification and characterization of E. coli, RNase E and the factors that could have an influence on the activity of the RNA-degrading enzymes, concretely, PNPase. It was found while two of its major compounds were being studied. The composition of this multienzyme may vary depending on the organism. The multiprotein complex RNA degradosome in E. coli consists of 4 canonical components: There are some alternate forms of the RNA degradosome with different proteins that have been reported. Supplementary alternate degradosome components are PcnB (poly A polymerase) and the RNA helicases RhlE and SrmB. Other alternate components during cold shock include RNA helicase CsdA. Additional alternate degradosome components during stationary phase include Rnr (RNase R) and the putative RNA helicase HrpA. Ppk (polyphosphate kinase) is another constituent that has been reported to be part of the complex, the same as RNA chaperone Hfq, PAP (prostatic acid phosphatase), other kinds of chaperones and ribosomal proteins. These have been found in cell-extracted degradosome preparations from E. coli. The structure of RNA degradosome is not as rigid as it seems to be in the picture because this one is only a model to understand how it works. The RNA degradosome's structure is dynamic and each component interacts with the components that are close to it. So the structure is like a molecular domain where RNA can interact as a substrate with each of the components and when this happens, it is really difficult for RNA to scape from the complex. The RNA degradosome is a huge multi-enzyme association that is involved in RNA metabolism and post-transcriptional control of gene expression in numerous bacteria such as Escherichia coli and Pseudoalteromonas haloplanktis. The multi-protein complex also serves as a machine for processing structured RNA precursors in the course of their maturation. RNA helicase is considered to help in the process of degradation to develop the double helix structure in RNA stem-loops. Occasionally, copurification of rRNA with degradosome is appreciated, which suggests that the complex may take part in rRNA and mRNA degradation. There is very few clear information about the role of degradosome. Looking into the steps of the degradation of a transcript in E. coli, what is known is that in the first place the endoribonucleases can cleave the substracts so that later on the exoribonucleases can work on the products. RhIB has very little activity by itself but the interaction with RNAse E can stimulate it. The role of enolase in the degradation process of RNA is still not properly described, apparently it helps the complex to be more specific during the process of degradation.