Chapter category: RNA
Short Interfering and MicroRNAs: Tiny but Mighty
Noncoding RNAs: Molecular Biology and Molecular Medicine
Edited by: Jan Barciszewski and Volker A. ErdmannISBN: 0-306-47835-8
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Chapter authors:
Martin Tabler, Alexandra Boutla, Kriton Kalantidis and Tsagris Mina
Two functionally distinct classes of short noncoding RNAs consisting of ca. 20-25 nucleotides have been discovered recently. Both classes of RNAs are generated from longer single- or double-stranded RNA precursors by the same ribonuclease. Either of the two categories of short RNAs is involved in posttranscriptional regulation of target RNAs that are in part or fully complementary. Despite a great degree of similarity, the two classes of RNAs are generated in different pathways and have different functions as well as different effects on their target RNAs. MicroRNAs (miRNAs) modulate translation efficiency in a reversible interaction with their cognate target mRNA, while short interfering RNA (siRNA) direct the specific degradation of their matching RNA target in a process called RNA interference (RNAi) or posttranscriptional gene silencing (PTGS). The current knowledge about origin, functionality of these two categories of small noncoding RNAs is summarized and first attempts towards practical application in gene suppression are reviewed. Peptides and RNA share some common features. Composed of amino acids or ribonucleotides they form polymeric macromolecules, that are usually linear, unbranched chains of variable size. The sequence of their units determines their overall structure and dynamics, a precondition for the functionality in a living cell. A further remarkable similarity between the two classes of biomolecules is the enormous size range. Peptides may be extremely large, like Titin, which is composed about 28,000 amino acids with a molecular weight of about 3 MD and a length of about 1 µm (reviewed in ref. 1). Quite remarkably, viral RNA has a similar size limit for its monomeric units. Coronaviruses contain the longest known RNA genome with a chain length of about 30,000 nucleotides,2 but some mRNAs and their precursors can be considerably longer. The other side of the size spectrum is formed by minimal peptides consisting of just two or three amino acids that are responsible for various bioactivities. For example the di- and tripeptides Pro-Gly (PG), Gly-Pro (GP), Pro-Gly-Pro (PGP) are members of the glyproline family that are involved—besides further activities - in suppression of some reactions of blood coagulation.3 Similar to small peptides, there are at least two classes of petite noncoding RNAs: the ‘short interfering RNA (siRNA)’ and the ‘microRNA (miRNA)’. Both types of RNAs have been discovered recently. They share common features, but exhibit also different function and are subject of this review.
Martin Tabler
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, University of Crete, Heraklion/Crete, Greece
Alexandra Boutla
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, University of Crete, Heraklion/Crete, Greece
Kriton Kalantidis
Institute for Molecular Biology and Biotechnology, Foundation for Research and Technology, University of Crete, Heraklion/Crete, Greece
Tsagris Mina
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Department of Biology,
University of Crete, Heraklion/Crete
GREECE
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