Generation and action of siRNAs and miRNAs


Summary

Micro RNAs and small interfering RNAs play crucial roles in regulating mRNA stability and translation in multicellular organisms. Micro RNAs derive from actual genes, are transcribed by RNA Polyas 2, and undergo cleavage to form a micro RNA duplex. They bind to target RNAs, guiding interactions and recruiting factors that contribute to mRNA destabilization. On the other hand, small interfering RNAs, originating from double-stranded RNA, can be synthetically introduced into cells to cleave target RNAs through an endonuclease complex, facilitating degradation. These processes are essential for precise gene regulation at the post-transcriptional level.


Regulation by Micro RNAs

Micro RNAs and small interfering RNAs regulate mRNA stability and translation with differences in origin, processing, targets, and mechanism of action.

Micro RNA Processing

Micro RNAs derive from actual genes in multicellular animals and plants, starting as primary transcripts transcribed by RNA Polyas 2. The primary transcript folds into a stem with unpaired nucleotides, undergoes cleavage by an enzyme complex, and is exported to the cytoplasm for further processing.

Micro RNA Structure

Micro RNA transcripts fold into a stem-loop structure with unpaired nucleotides and single-stranded extensions at both ends, serving as substrates for cleavage by an enzyme complex.

Micro RNA Duplex Formation

The pre-micro RNA transcript is processed by nuclear export factors and enzymes to generate a micro RNA duplex, with one strand acting as the guide and the other as the passenger, determining target specificity.

Micro RNA Target Binding

Micro RNAs bind to target RNAs, particularly in the 3' UTRs of mRNAs, with the seed region (positions 2 to 8) of the micro RNA guiding the interaction and binding to the P domain of the Argonaute protein.

Micro RNA Repression Activity

Micro RNAs, when bound to the Argonaute protein, recruit additional factors and contribute to MRNA destabilization. The repression activity of Argonaute is crucial for micro RNA-mediated gene regulation.

Small Interfering RNA Processing

Small interfering RNAs are derived from double-stranded RNA and can arise from various sources, including viral RNAs. These RNAs can be introduced synthetically into cells for specific purposes and undergo processing to form short duplex RNAs.

Small Interfering RNA Mechanism

Small interfering RNAs are processed by an endogenous endonuclease complex, leading to cleavage of target RNAs. The slicing reaction results in products that are targeted for degradation through the exosome pathway.

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