Before learning how siRNA and miRNA are similar and different, it’s first important to understand just what they are. To start, both siRNA and miRNA are proteomics tools used to study various aspects of gene expression. Proteomics is the study of proteins by which a cell’s complete complement of proteins is examined at once.
Now that you know what siRNA and miRNA are, you may still want to know if they are similar or different. Well, the jury’s somewhat out on that matter. Depending on the source, you may find information stating that siRNA and miRNA are the same thing–or separate entities entirely.
Why the disagreement? Well, for starters, the two are both formed in the same manner. They emerge from longer RNA precursors. They are also processed in the cytoplasm by an enzymecalled Dicer before becoming part of the protein complex called RISC. So, what is the difference between siRNA and miRNA, or is there any difference at all?
Slight Differences Between the Two
The process of RNA interference (RNAi) can be moderated by either siRNA or miRNA, but there are subtle differences between the two. As mentioned above, both are processed inside the cell by the enzyme called Dicer and incorporated into a complex called RISC.
siRNA is considered exogenous double-stranded RNA that is taken up by cells. In other words, it enters via vectors such as viruses. Vectors arise when geneticists use bits of DNA to clone a gene to produce a genetically modified organism (GMO).
The DNA used in this process is called a vector.
While siRNA is thought to be exogenous double-stranded RNA, miRNA,on the other hand, is single stranded and comes from endogenous (made inside the cell) non-coding RNA that is found within the introns of larger RNA molecules.
Another difference is that in animals, siRNA typically binds perfectly to its mRNA target. It is a perfect match to the sequence. In contrast, miRNA can inhibit translation of many different mRNA sequences because its pairing is imperfect. Translation occurs after messenger RNA is altered and binds to a particular site on a ribosome. In plants, miRNA tends to have a more perfectly complementary sequence which induces mRNA cleavage as opposed to just repression of translation.
Both siRNA and miRNA can play a role in epigenetics through a process called RNA-induced transcriptional silencing (RITS). Epigenetics is the study of heritable genetic information in which the nucleotide sequence of DNA is not altered but manifested as chemical marks that are added to DNA or chromatin proteins after replication. Likewise, both are important targets for therapeutic use, because of the roles they play in the controlling gene expression.