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A new way to get rid of old RNA

Cells are under constant degradation and renewal and so are their intracellular constituents. Scientists have discovered a novel and conserved pathway for nucleic acid degradation with implications for regulation and signalling.
A new way to get rid of old RNA
Ribonucleic acids (RNAs) are the transcribed copies of small segments of deoxyribonucleic acid (DNA). As such, they play numerous roles in the cell, including information transmission and regulation of cellular activities.

Build-up of RNA in the cell would be toxic so there is complex RNA degradation machinery, many of whose mechanisms appear to be highly conserved. The bacteria Escherichia coli (E. coli) and the eukaryotic yeast Schizosaccharomyces pombe (S. pombe) are common models for the study of many cellular processes, and RNA degradation is no exception.

However, many mysteries remain regarding RNases, enzymes that catalyse the cleavage or degradation of RNAs, and more general nucleases that cleave nucleic acids. The EU-funded project 'Spatial organisation and dynamics of Escherichia coli RNA degradation machinery' (RNASEDYNAMICS) addressed this issue.

Project scientists developed various E. coli strains with different RNases and RNA metabolism proteins. Exploiting fluorescence techniques and others for the purification of bound complexes, the researchers demonstrated that RNase R binds to cellular ribosomes, suggesting a role in degradation of ribosomal RNAs.

Recently, a new S. pombe nuclease belonging to the RNase II family of enzymes was discovered that appeared to be homologous with a human one, DIS3L2, one of the three DIS3 isoforms in humans together with DIS3 and DIS3L. RNASEDYNAMICS proved that the new yeast nuclease does in fact belong to the same family as the human one. Further, DIS3 has been shown to form a complex with the exosome degradation machinery in the final step of one of two pathways to messenger RNA (mRNA) degradation. Scientists demonstrated that in S. Pombe DIS3L2 degrades RNA independently of the exosome machinery, revealing a new eukaryotic degradation pathway in the cytoplasm. These results will be published in the highly esteemed The EMBO Journal.

RNA degradation is one of the most important processes in living cells, contributing to cell stability as well as the production of regulatory molecules. Understanding the mechanisms could provide important insight into cell homeostasis with the potential for therapeutic benefits.

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