siRNA vs miRNA
RNAs are very important molecules, which help to build up the life of organisms. Recently scientists have discovered small RNAs called RNA interference or RNAi, which act after the transcription to control gene expression. The two major types of small RNAs are micro RNA or miRNA and small interfering RNA or siRNA. These molecules basically regulate the gene expression by suppressing the target gene. Both miRNA and siRNA have very similar biogenesis pathways, though there are some differences exist between them. The origin of miRNA and siRNA are from dsRNA molecules. Mature miRNAs are structurally similar to siRNA molecules.
Micro RNAs or miRNAs are the small RNA molecules which mediate the final check in translational gene regulation. Deregulation of miRNA may lead to cancer and other disease development. Therefore, the proper regulation of information encoded in the non-coding region of miRNA is very critical in many fundamental cellular processes.
siRNAs are also referred to as short interfering or silencing RNA and are made up of double stranded RNA with 20 to 25 base pairs. The main role of siRNA is to interfere with the expression of specific genes with complementary nucleotide sequences. siRNA is made up of short double-stranded RNA with phosphorylated 5’ ends and hydroxylated 3’ ends with two overhanging nucleotides.
What is the difference between siRNA and miRNA?
• miRNA derived from specific genomic loci, while siRNA derived from mRNA, transposons, viruses or heterochromatic DNA.
• Synthesis of miRNA is processed from longer precursor hairpin transcripts (primary nuclear miRNA sequence by RNase III endonuclease), whereas that of siRNA processed from long bimolecular RNA duplexes.
• Each miRNA hairpin precursor molecule produces single miRNA duplex, whereas each siRNA precursor molecule produces multiple siRNA duplexes.
• siRNA sequences are rarely conserved, while miRNA sequences are well conserved.
• All bases within siRNA contribute to its target specificity, whereas only 5’ half of miRNA contributes to its target specificity.
• miRNA often bind to the 3’ untranslated region of target transcripts, whereas siRNAs form complementary duplex anywhere along a target mRNA.
• miRNA specify ‘hetero- silencing’ while siRNA used for ‘auto silencing’.
• miRNA acts as a signal to prevent translation, whereas siRNA physically prevents translation.