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Small RNA: A Comprehensive Overview
Introduction
Various types of small RNAs (sRNAs) have been identified and extensively studied, leading to advancements in the field of molecular biology. These sRNAs play essential roles in regulating gene expression and maintaining cellular homeostasis.
Classification and Mechanisms of Biogenesis
sRNAs can be classified based on their biogenesis pathways: *
MicroRNAs (miRNAs):
20-30 nucleotides long, miRNAs are derived from short hairpin RNA (shRNA) precursors. They bind to the 3' untranslated regions (UTRs) of target mRNAs, leading to translational repression or mRNA degradation.
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Small Interfering RNAs (siRNAs):
Also 20-30 nucleotides long, siRNAs have a distinct biogenesis pathway. They are typically generated from long double-stranded RNA (dsRNA) by an enzyme called Dicer and guide the RISC complex to target mRNAs for degradation.
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PIWI-Interacting RNAs (piRNAs):
Larger than miRNAs and siRNAs, piRNAs are produced from specific genomic loci and interact with PIWI proteins. They primarily regulate transposon activity in germline cells.
Molecular Functions
sRNAs exert their molecular functions through various mechanisms: *
Gene Regulation:
miRNAs and siRNAs bind to target mRNAs, resulting in translational inhibition, mRNA decay, or modification of mRNA stability.
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Chromatin Modification:
Some sRNAs, such as piRNAs, can bind to specific genomic regions and guide chromatin modifications, influencing gene expression patterns.
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Silencing of Transposable Elements:
piRNAs are particularly adept at suppressing the activity of transposable elements, which are mobile genetic elements that could disrupt genome stability.
Implications and Research
The discovery of sRNAs has had a profound impact on our understanding of gene regulation and cellular processes. Ongoing research focuses on: * Exploiting sRNAs for therapeutic applications * Understanding the role of sRNAs in complex biological systems * Developing novel technologies for manipulating sRNA expression and function