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MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. miRNAs base-pair to complementary sequences in mRNA molecules, then gene silence said mRNA molecules by one or more of the following processes:
- Cleavage of mRNA strand into two pieces,
- Destabilization of mRNA by shortening its poly(A) tail, or
- Translation of mRNA into proteins.
A non-coding RNA (ncRNA) is a functional RNA molecule that is not translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Abundant and functionally important types of non-coding RNAs include transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), as well as small RNAs such as microRNAs, siRNAs, piRNAs, snoRNAs, snRNAs, exRNAs, scaRNAs and the long ncRNAs such as Xist and HOTAIR.
Small RNA (sRNA) are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding. RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA. Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA). Small RNA "is unable to induce RNAi alone, and to accomplish the task it must form the core of the RNA–protein complex termed the RNA-induced silencing complex (RISC), specifically with Argonaute protein".
Dicer, also known as endoribonuclease Dicer or helicase with RNase motif, is an enzyme that in humans is encoded by the DICER1 gene. Being part of the RNase III family, Dicer cleaves double-stranded RNA (dsRNA) and pre-microRNA (pre-miRNA) into short double-stranded RNA fragments called small interfering RNA and microRNA, respectively. These fragments are approximately 20–25 base pairs long with a two-base overhang on the 3′-end. Dicer facilitates the activation of the RNA-induced silencing complex (RISC), which is essential for RNA interference. RISC has a catalytic component Argonaute, which is an endonuclease capable of degrading messenger RNA (mRNA).
In molecular biology, small nucleolar RNAs (snoRNAs) are a class of small RNA molecules that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs. There are two main classes of snoRNA, the C/D box snoRNAs, which are associated with methylation, and the H/ACA box snoRNAs, which are associated with pseudouridylation. SnoRNAs are commonly referred to as guide RNAs but should not be confused with the guide RNAs that direct RNA editing in trypanosomes or the guide RNAs (gRNAs) used by Cas9 for CRISPR gene editing.
Ribonuclease III (RNase III or RNase C)(BRENDA 3.1.26.3) is a type of ribonuclease that recognizes dsRNA and cleaves it at specific targeted locations to transform them into mature RNAs. These enzymes are a group of endoribonucleases that are characterized by their ribonuclease domain, which is labelled the RNase III domain. They are ubiquitous compounds in the cell and play a major role in pathways such as RNA precursor synthesis, RNA Silencing, and the pnp autoregulatory mechanism.
Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the DROSHA gene. It is the primary nuclease that executes the initiation step of miRNA processing in the nucleus. It works closely with DGCR8 and in correlation with Dicer. It has been found significant in clinical knowledge for cancer prognosis and HIV-1 replication.
The miR-29 microRNA precursor, or pre-miRNA, is a small RNA molecule in the shape of a stem-loop or hairpin. Each arm of the hairpin can be processed into one member of a closely related family of short non-coding RNAs that are involved in regulating gene expression. The processed, or "mature" products of the precursor molecule are known as microRNA (miRNA), and have been predicted or confirmed in a wide range of species.
miR-30 microRNA precursor is a small non-coding RNA that regulates gene expression. Animal microRNAs are transcribed as pri-miRNA of varying length which in turns are processed in the nucleus by Drosha into ~70 nucleotide stem-loop precursor called pre-miRNA and subsequently processed by the Dicer enzyme to give a mature ~22 nucleotide product. In this case the mature sequence comes from both the 3' (miR-30) and 5' (mir-97-6) arms of the precursor. The products are thought to have regulatory roles through complementarity to mRNA.
Small Cajal body specific RNA 15 is a small nucleolar RNA found in Cajal bodies and believed to be involved in the pseudouridylation of U1 spliceosomal RNA.
In molecular biology, Small Nucleolar RNA SNORD93 is a non-coding RNA (ncRNA) molecule that functions in the biogenesis (modification) of other small nuclear RNAs (snRNAs). This type of modifying RNA is located in the nucleolus of the Eukaryotic cell which is a major site of snRNA biogenesis. It is known as a small nucleolar RNA (snoRNA) and is also often referred to as a guide RNA.
In molecular biology, Small Nucleolar RNA SNORD88 is a non-coding RNA (ncRNA) molecule which functions in the biogenesis (modification) of other small nuclear RNAs (snRNAs). This type of modifying RNA is located in the nucleolus of the eukaryotic cell which is a major site of snRNA biogenesis. It is known as a small nucleolar RNA (snoRNA) and also often referred to as a guide RNA.
Mirtrons are a type of microRNAs that are located in the introns of the mRNA encoding host genes. These short hairpin introns formed via atypical miRNA biogenesis pathways. Mirtrons arise from the spliced-out introns and are known to function in gene expression.
MicroRNAs (miR) are small non-coding RNAs that regulate gene expression at the posttranscriptional level. MiR cluster 23/27/24 regulates angiogenesis, which is the process of forming new blood vessels by deposition of endothelial cells. There are 2 types of miR-27s found on endothelial cells: miR-27a and miR-27b. The actual mechanisms of miR-27s are not well known, but studies showed that overexpression of miR-27b increases angiogenesis. These results suggest that miR27b might be useful for treating patients with ischemic heart disease.
The microprocessor complex is a protein complex involved in the early stages of processing microRNA (miRNA) and RNA interference (RNAi) in animal cells. The complex is minimally composed of the ribonuclease enzyme Drosha and the dimeric RNA-binding protein DGCR8, and cleaves primary miRNA substrates to pre-miRNA in the cell nucleus. Microprocessor is also the smaller of the two multi-protein complexes that contain human Drosha.
MicroRNA 203a is a small RNA that in humans is encoded by the preMIR203A gene.
MicroRNA 223 is a protein that in humans is encoded by the MIR223 gene.
Small nucleolar RNA host gene 1 is a non-protein coding RNA that in humans is encoded by the SNHG1 gene.
MicroRNA 93 is a functional RNA and a microRNA that in humans is encoded by the MIR93 gene.
A majority of the human genome is made up of non-protein coding DNA. It infers that such sequences are not commonly employed to encode for a protein. However, even though these regions do not code for protein, they have other functions and carry necessary regulatory information.They can be classified based on the size of the ncRNA. Small noncoding RNA is usually categorized as being under 200 bp in length, whereas long noncoding RNA is greater than 200bp. In addition, they can be categorized by their function within the cell; Infrastructural and Regulatory ncRNAs. Infrastructural ncRNAs seem to have a housekeeping role in translation and splicing and include species such as rRNA, tRNA, snRNA.Regulatory ncRNAs are involved in the modification of other RNAs.
References
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- ↑ Ender C, Krek A, Friedländer MR, Beitzinger M, Weinmann L, Chen W, et al. (2008). "A human snoRNA with microRNA-like functions". Mol Cell. 32 (4): 519–528. doi: 10.1016/j.molcel.2008.10.017 . PMID 19026782.
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- ↑ Kiss-László Z, Henry Y, Kiss T (1998). "Sequence and structural elements of methylation guide snoRNAs essential for site-specific ribose methylation of pre-rRNA". EMBO J. 17 (3): 797–807. doi:10.1093/emboj/17.3.797. PMC 1170428 . PMID 9451004.
- ↑ Li W, Saraiya AA, Wang CC (2011). "Gene regulation in Giardia lambia involves a putative microRNA derived from a small nucleolar RNA". PLOS Negl Trop Dis. 5 (10): e1338. doi: 10.1371/journal.pntd.0001338 . PMC 3196473 . PMID 22028939.
- 1 2 Li W, Saraiya AA, Wang CC (2012). "The profile of snoRNA-derived microRNAs that regulate expression of variant surface proteins in Giardia lamblia". Cell Microbiol. 14 (9): 1455–1473. doi:10.1111/j.1462-5822.2012.01811.x. PMC 3422372 . PMID 22568619.