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.
The number of non-coding RNAs within the human genome is unknown; however, recent transcriptomic and bioinformatic studies suggest that there are thousands of non-coding transcripts. [1] [2] [3] [4] [5] [6] [7] Many of the newly identified ncRNAs have unknown functions, if any. [8] There is no consensus on how much of non-coding transcription is functional: some believe most ncRNAs to be non-functional "junk RNA", spurious transcriptions, [9] [10] while others expect that many non-coding transcripts have functions to be discovered. [11] [12]
Nucleic acids were first discovered in 1868 by Friedrich Miescher, [13] and by 1939, RNA had been implicated in protein synthesis. [14] Two decades later, Francis Crick predicted a functional RNA component which mediated translation; he reasoned that RNA is better suited to base-pair with an mRNA transcript than a pure polypeptide. [15]
The first non-coding RNA to be characterised was an alanine tRNA found in baker's yeast, its structure was published in 1965. [16] To produce a purified alanine tRNA sample, Robert W. Holley et al. used 140kg of commercial baker's yeast to give just 1g of purified tRNAAla for analysis. [17] The 80 nucleotide tRNA was sequenced by first being digested with Pancreatic ribonuclease (producing fragments ending in Cytosine or Uridine) and then with takadiastase ribonuclease Tl (producing fragments which finished with Guanosine). Chromatography and identification of the 5' and 3' ends then helped arrange the fragments to establish the RNA sequence. [17] Of the three structures originally proposed for this tRNA, [16] the 'cloverleaf' structure was independently proposed in several following publications. [18] [19] [20] [21] The cloverleaf secondary structure was finalised following X-ray crystallography analysis performed by two independent research groups in 1974. [22] [23]
Ribosomal RNA was next to be discovered, followed by URNA in the early 1980s. Since then, the discovery of new non-coding RNAs has continued with snoRNAs, Xist, CRISPR and many more. [24] Recent notable additions include riboswitches and miRNA; the discovery of the RNAi mechanism associated with the latter earned Craig C. Mello and Andrew Fire the 2006 Nobel Prize in Physiology or Medicine. [25]
Recent discoveries of ncRNAs have been achieved through both experimental and bioinformatic methods.
Noncoding RNAs belong to several groups and are involved in many cellular processes. [26] These range from ncRNAs of central importance that are conserved across all or most cellular life through to more transient ncRNAs specific to one or a few closely related species. The more conserved ncRNAs are thought to be molecular fossils or relics from the last universal common ancestor and the RNA world, and their current roles remain mostly in regulation of information flow from DNA to protein. [27] [28] [29]
Many of the conserved, essential and abundant ncRNAs are involved in translation. Ribonucleoprotein (RNP) particles called ribosomes are the 'factories' where translation takes place in the cell. The ribosome consists of more than 60% ribosomal RNA; these are made up of 3 ncRNAs in prokaryotes and 4 ncRNAs in eukaryotes. Ribosomal RNAs catalyse the translation of nucleotide sequences to protein. Another set of ncRNAs, Transfer RNAs, form an 'adaptor molecule' between mRNA and protein. The H/ACA box and C/D box snoRNAs are ncRNAs found in archaea and eukaryotes. RNase MRP is restricted to eukaryotes. Both groups of ncRNA are involved in the maturation of rRNA. The snoRNAs guide covalent modifications of rRNA, tRNA and snRNAs; RNase MRP cleaves the internal transcribed spacer 1 between 18S and 5.8S rRNAs. The ubiquitous ncRNA, RNase P, is an evolutionary relative of RNase MRP. [31] RNase P matures tRNA sequences by generating mature 5'-ends of tRNAs through cleaving the 5'-leader elements of precursor-tRNAs. Another ubiquitous RNP called SRP recognizes and transports specific nascent proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. In bacteria, Transfer-messenger RNA (tmRNA) is an RNP involved in rescuing stalled ribosomes, tagging incomplete polypeptides and promoting the degradation of aberrant mRNA.[ citation needed ]
In eukaryotes, the spliceosome performs the splicing reactions essential for removing intron sequences, this process is required for the formation of mature mRNA. The spliceosome is another RNP often known as the snRNP or tri-snRNP. There are two different forms of the spliceosome, the major and minor forms. The ncRNA components of the major spliceosome are U1, U2, U4, U5, and U6. The ncRNA components of the minor spliceosome are U11, U12, U5, U4atac and U6atac.[ citation needed ]
Another group of introns can catalyse their own removal from host transcripts; these are called self-splicing RNAs. There are two main groups of self-splicing RNAs: group I catalytic intron and group II catalytic intron. These ncRNAs catalyze their own excision from mRNA, tRNA and rRNA precursors in a wide range of organisms.[ citation needed ]
In mammals it has been found that snoRNAs can also regulate the alternative splicing of mRNA, for example snoRNA HBII-52 regulates the splicing of serotonin receptor 2C. [32]
In nematodes, the SmY ncRNA appears to be involved in mRNA trans-splicing. [33]
Y RNAs are stem loops, necessary for DNA replication through interactions with chromatin and initiation proteins (including the origin recognition complex). [35] [36] They are also components of the Ro60 ribonucleoprotein particle [37] which is a target of autoimmune antibodies in patients with systemic lupus erythematosus. [38]
The expression of many thousands of genes are regulated by ncRNAs. This regulation can occur in trans or in cis. There is increasing evidence that a special type of ncRNAs called enhancer RNAs, transcribed from the enhancer region of a gene, act to promote gene expression.[ citation needed ]
In higher eukaryotes microRNAs regulate gene expression. A single miRNA can reduce the expression levels of hundreds of genes. The mechanism by which mature miRNA molecules act is through partial complementarity to one or more messenger RNA (mRNA) molecules, generally in 3' UTRs. The main function of miRNAs is to down-regulate gene expression.
The ncRNA RNase P has also been shown to influence gene expression. In the human nucleus, RNase P is required for the normal and efficient transcription of various ncRNAs transcribed by RNA polymerase III. These include tRNA, 5S rRNA, SRP RNA, and U6 snRNA genes. RNase P exerts its role in transcription through association with Pol III and chromatin of active tRNA and 5S rRNA genes. [39]
It has been shown that 7SK RNA, a metazoan ncRNA, acts as a negative regulator of the RNA polymerase II elongation factor P-TEFb, and that this activity is influenced by stress response pathways.[ citation needed ]
The bacterial ncRNA, 6S RNA, specifically associates with RNA polymerase holoenzyme containing the sigma70 specificity factor. This interaction represses expression from a sigma70-dependent promoter during stationary phase.[ citation needed ]
Another bacterial ncRNA, OxyS RNA represses translation by binding to Shine-Dalgarno sequences thereby occluding ribosome binding. OxyS RNA is induced in response to oxidative stress in Escherichia coli.[ citation needed ]
The B2 RNA is a small noncoding RNA polymerase III transcript that represses mRNA transcription in response to heat shock in mouse cells. B2 RNA inhibits transcription by binding to core Pol II. Through this interaction, B2 RNA assembles into preinitiation complexes at the promoter and blocks RNA synthesis. [40]
A recent study has shown that just the act of transcription of ncRNA sequence can have an influence on gene expression. RNA polymerase II transcription of ncRNAs is required for chromatin remodelling in the Schizosaccharomyces pombe. Chromatin is progressively converted to an open configuration, as several species of ncRNAs are transcribed. [41]
A number of ncRNAs are embedded in the 5' UTRs (Untranslated Regions) of protein coding genes and influence their expression in various ways. For example, a riboswitch can directly bind a small target molecule; the binding of the target affects the gene's activity.[ citation needed ]
RNA leader sequences are found upstream of the first gene of amino acid biosynthetic operons. These RNA elements form one of two possible structures in regions encoding very short peptide sequences that are rich in the end product amino acid of the operon. A terminator structure forms when there is an excess of the regulatory amino acid and ribosome movement over the leader transcript is not impeded. When there is a deficiency of the charged tRNA of the regulatory amino acid the ribosome translating the leader peptide stalls and the antiterminator structure forms. This allows RNA polymerase to transcribe the operon. Known RNA leaders are Histidine operon leader, Leucine operon leader, Threonine operon leader and the Tryptophan operon leader.[ citation needed ]
Iron response elements (IRE) are bound by iron response proteins (IRP). The IRE is found in UTRs of various mRNAs whose products are involved in iron metabolism. When iron concentration is low, IRPs bind the ferritin mRNA IRE leading to translation repression.[ citation needed ]
Internal ribosome entry sites (IRES) are RNA structures that allow for translation initiation in the middle of a mRNA sequence as part of the process of protein synthesis.[ citation needed ]
Piwi-interacting RNAs (piRNAs) expressed in mammalian testes and somatic cells form RNA-protein complexes with Piwi proteins. These piRNA complexes (piRCs) have been linked to transcriptional gene silencing of retrotransposons and other genetic elements in germline cells, particularly those in spermatogenesis.
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) are repeats found in the DNA of many bacteria and archaea. The repeats are separated by spacers of similar length. It has been demonstrated that these spacers can be derived from phage and subsequently help protect the cell from infection.
Telomerase is an RNP enzyme that adds specific DNA sequence repeats ("TTAGGG" in vertebrates) to telomeric regions, which are found at the ends of eukaryotic chromosomes. The telomeres contain condensed DNA material, giving stability to the chromosomes. The enzyme is a reverse transcriptase that carries Telomerase RNA, which is used as a template when it elongates telomeres, which are shortened after each replication cycle.
Xist (X-inactive-specific transcript) is a long ncRNA gene on the X chromosome of the placental mammals that acts as major effector of the X chromosome inactivation process forming Barr bodies. An antisense RNA, Tsix, is a negative regulator of Xist. X chromosomes lacking Tsix expression (and thus having high levels of Xist transcription) are inactivated more frequently than normal chromosomes. In drosophilids, which also use an XY sex-determination system, the roX (RNA on the X) RNAs are involved in dosage compensation. [42] Both Xist and roX operate by epigenetic regulation of transcription through the recruitment of histone-modifying enzymes.
Bifunctional RNAs, or dual-function RNAs, are RNAs that have two distinct functions. [43] [44] The majority of the known bifunctional RNAs are mRNAs that encode both a protein and ncRNAs. However, a growing number of ncRNAs fall into two different ncRNA categories; e.g., H/ACA box snoRNA and miRNA. [45] [46]
Two well known examples of bifunctional RNAs are SgrS RNA and RNAIII. However, a handful of other bifunctional RNAs are known to exist (e.g., steroid receptor activator/SRA, [47] VegT RNA, [48] [49] Oskar RNA, [50] ENOD40, [51] p53 RNA [52] SR1 RNA, [53] and Spot 42 RNA. [54] ) Bifunctional RNAs were the subject of a 2011 special issue of Biochimie. [55]
There is an important link between certain non-coding RNAs and the control of hormone-regulated pathways. In Drosophila , hormones such as ecdysone and juvenile hormone can promote the expression of certain miRNAs. Furthermore, this regulation occurs at distinct temporal points within Caenorhabditis elegans development. [56] In mammals, miR-206 is a crucial regulator of estrogen-receptor-alpha. [57]
Non-coding RNAs are crucial in the development of several endocrine organs, as well as in endocrine diseases such as diabetes mellitus. [58] Specifically in the MCF-7 cell line, addition of 17β-estradiol increased global transcription of the noncoding RNAs called lncRNAs near estrogen-activated coding genes. [59]
C. elegans was shown to learn and inherit pathogenic avoidance after exposure to a single non-coding RNA of a bacterial pathogen. [60] [61]
As with proteins, mutations or imbalances in the ncRNA repertoire within the body can cause a variety of diseases.
Many ncRNAs show abnormal expression patterns in cancerous tissues. [6] These include miRNAs, long mRNA-like ncRNAs, [62] [63] GAS5, [64] SNORD50, [65] telomerase RNA and Y RNAs. [66] The miRNAs are involved in the large scale regulation of many protein coding genes, [67] [68] the Y RNAs are important for the initiation of DNA replication, [35] telomerase RNA that serves as a primer for telomerase, an RNP that extends telomeric regions at chromosome ends (see telomeres and disease for more information). The direct function of the long mRNA-like ncRNAs is less clear.
Germline mutations in miR-16-1 and miR-15 primary precursors have been shown to be much more frequent in patients with chronic lymphocytic leukemia compared to control populations. [69] [70]
It has been suggested that a rare SNP (rs11614913) that overlaps hsa-mir-196a-2 has been found to be associated with non-small cell lung carcinoma. [71] Likewise, a screen of 17 miRNAs that have been predicted to regulate a number of breast cancer associated genes found variations in the microRNAs miR-17 and miR-30c-1of patients; these patients were noncarriers of BRCA1 or BRCA2 mutations, lending the possibility that familial breast cancer may be caused by variation in these miRNAs. [72] The p53 tumor suppressor is arguably the most important agent in preventing tumor formation and progression. The p53 protein functions as a transcription factor with a crucial role in orchestrating the cellular stress response. In addition to its crucial role in cancer, p53 has been implicated in other diseases including diabetes, cell death after ischemia, and various neurodegenerative diseases such as Huntington, Parkinson, and Alzheimer. Studies have suggested that p53 expression is subject to regulation by non-coding RNA. [5]
Another example of non-coding RNA dysregulated in cancer cells is the long non-coding RNA Linc00707. Linc00707 is upregulated and sponges miRNAs in human bone marrow-derived mesenchymal stem cells, [73] gastric cancer [74] or breast cancer, [75] [76] and thus promotes osteogenesis, contributes to hepatocellular carcinoma progression, promotes proliferation and metastasis, or indirectly regulates expression of proteins involved in cancer aggressiveness, respectively.
The deletion of the 48 copies of the C/D box snoRNA SNORD116 has been shown to be the primary cause of Prader–Willi syndrome. [77] [78] [79] [80] Prader–Willi is a developmental disorder associated with over-eating and learning difficulties. SNORD116 has potential target sites within a number of protein-coding genes, and could have a role in regulating alternative splicing. [81]
The chromosomal locus containing the small nucleolar RNA SNORD115 gene cluster has been duplicated in approximately 5% of individuals with autistic traits. [82] [83] A mouse model engineered to have a duplication of the SNORD115 cluster displays autistic-like behaviour. [84] A recent small study of post-mortem brain tissue demonstrated altered expression of long non-coding RNAs in the prefrontal cortex and cerebellum of autistic brains as compared to controls. [85]
Mutations within RNase MRP have been shown to cause cartilage–hair hypoplasia, a disease associated with an array of symptoms such as short stature, sparse hair, skeletal abnormalities and a suppressed immune system that is frequent among Amish and Finnish. [86] [87] [88] The best characterised variant is an A-to-G transition at nucleotide 70 that is in a loop region two bases 5' of a conserved pseudoknot. However, many other mutations within RNase MRP also cause CHH.
The antisense RNA, BACE1-AS is transcribed from the opposite strand to BACE1 and is upregulated in patients with Alzheimer's disease. [89] BACE1-AS regulates the expression of BACE1 by increasing BACE1 mRNA stability and generating additional BACE1 through a post-transcriptional feed-forward mechanism. By the same mechanism it also raises concentrations of beta amyloid, the main constituent of senile plaques. BACE1-AS concentrations are elevated in subjects with Alzheimer's disease and in amyloid precursor protein transgenic mice.
Variation within the seed region of mature miR-96 has been associated with autosomal dominant, progressive hearing loss in humans and mice. The homozygous mutant mice were profoundly deaf, showing no cochlear responses. Heterozygous mice and humans progressively lose the ability to hear. [90] [91] [92]
A number of mutations within mitochondrial tRNAs have been linked to diseases such as MELAS syndrome, MERRF syndrome, and chronic progressive external ophthalmoplegia. [93] [94] [95] [96]
Scientists have started to distinguish functional RNA (fRNA) from ncRNA, to describe regions functional at the RNA level that may or may not be stand-alone RNA transcripts. [97] [98] [99] This implies that fRNA (such as riboswitches, SECIS elements, and other cis-regulatory regions) is not ncRNA. Yet fRNA could also include mRNA, as this is RNA coding for protein, and hence is functional. Additionally artificially evolved RNAs also fall under the fRNA umbrella term. Some publications [24] state that ncRNA and fRNA are nearly synonymous, however others have pointed out that a large proportion of annotated ncRNAs likely have no function. [9] [10] It also has been suggested to simply use the term RNA, since the distinction from a protein coding RNA (messenger RNA) is already given by the qualifier mRNA. [100] This eliminates the ambiguity when addressing a gene "encoding a non-coding" RNA. Besides, there may be a number of ncRNAs that are misannoted in published literature and datasets. [101] [102] [103]
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself or by forming a template for the production of proteins. RNA and deoxyribonucleic acid (DNA) are nucleic acids. The nucleic acids constitute one of the four major macromolecules essential for all known forms of life. RNA is assembled as a chain of nucleotides. Cellular organisms use messenger RNA (mRNA) to convey genetic information that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome.
Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules. Other functional regions of the non-coding DNA fraction include regulatory sequences that control gene expression; scaffold attachment regions; origins of DNA replication; centromeres; and telomeres. Some non-coding regions appear to be mostly nonfunctional, such as introns, pseudogenes, intergenic DNA, and fragments of transposons and viruses. Regions that are completely nonfunctional are called junk DNA.
Micro ribonucleic acid are small, single-stranded, non-coding RNA molecules containing 21–23 nucleotides. Found in plants, animals, and even some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. miRNAs base-pair to complementary sequences in messenger RNA (mRNA) molecules, then silence said mRNA molecules by one or more of the following processes:
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, and ultimately affect a phenotype. These products are often proteins, but in non-protein-coding genes such as transfer RNA (tRNA) and small nuclear RNA (snRNA), the product is a functional non-coding RNA. The process of gene expression is used by all known life—eukaryotes, prokaryotes, and utilized by viruses—to generate the macromolecular machinery for life.
Regulation of gene expression, or gene regulation, includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products. Sophisticated programs of gene expression are widely observed in biology, for example to trigger developmental pathways, respond to environmental stimuli, or adapt to new food sources. Virtually any step of gene expression can be modulated, from transcriptional initiation, to RNA processing, and to the post-translational modification of a protein. Often, one gene regulator controls another, and so on, in a gene regulatory network.
Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded non-coding RNA molecules, typically 20–24 base pairs in length, similar to microRNA (miRNA), and operating within the RNA interference (RNAi) pathway. It interferes with the expression of specific genes with complementary nucleotide sequences by degrading messenger RNA (mRNA) after transcription, preventing translation. It was discovered in 1998 by Andrew Fire at the Carnegie Institution for Science in Washington, D.C. and Craig Mello at the University of Massachusetts in Worcester.
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).
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.
RNA silencing or RNA interference refers to a family of gene silencing effects by which gene expression is negatively regulated by non-coding RNAs such as microRNAs. RNA silencing may also be defined as sequence-specific regulation of gene expression triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are conserved among most eukaryotes. The most common and well-studied example is 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).
Long non-coding RNAs are a type of RNA, generally defined as transcripts more than 200 nucleotides that are not translated into protein. This arbitrary limit distinguishes long ncRNAs from small non-coding RNAs, such as microRNAs (miRNAs), small interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs), and other short RNAs. Given that some lncRNAs have been reported to have the potential to encode small proteins or micro-peptides, the latest definition of lncRNA is a class of RNA molecules of over 200 nucleotides that have no or limited coding capacity. Long intervening/intergenic noncoding RNAs (lincRNAs) are sequences of lncRNA which do not overlap protein-coding genes.
HOTAIR is a human gene located between HOXC11 and HOXC12 on chromosome 12. It is the first example of an RNA expressed on one chromosome that has been found to influence the transcription of the HOXD cluster posterior genes located on chromosome 2. The sequence and function of HOTAIR are different in humans and mice. Sequence analysis of HOTAIR revealed that it exists in mammals, has poorly conserved sequences and considerably conserved structures, and has evolved faster than nearby HoxC genes. A subsequent study identified HOTAIR has 32 nucleotides long conserved noncoding element (CNE) that has a paralogous copy in HOXD cluster region, suggesting that the HOTAIR conserved sequences predate whole genome duplication events at the root of vertebrate. While the conserved sequence paralogous with HOXD cluster is 32 nucleotide long, the HOTAIR sequence conserved from human to fish is about 200 nucleotide long and is marked by active enhancer features.
Growth arrest-specific 5 is a non-protein coding RNA that in humans is encoded by the GAS5 gene.
MALAT1-associated small cytoplasmic RNA, also known as mascRNA, is a non-coding RNA found in the cytosol. This is a small RNA, roughly 53–61 nucleotides in length, that is processed from a much longer ncRNA called MALAT1 by an enzyme called RNase P. This RNA is expressed in many different human tissues, is highly conserved by evolution and shares a remarkable similarity to tRNA which is also produced by RNase P, yet this RNA is not aminoacylated in HeLa cells. The primary transcript, MALAT1, appears to be upregulated in several malignant cancers. Another small RNA that is homologous to mascRNA, called menRNA, is processed from another long ncRNA called MEN beta.
Cryptic unstable transcripts (CUTs) are a subset of non-coding RNAs (ncRNAs) that are produced from intergenic and intragenic regions. CUTs were first observed in S. cerevisiae yeast models and are found in most eukaryotes. Some basic characteristics of CUTs include a length of around 200–800 base pairs, a 5' cap, poly-adenylated tail, and rapid degradation due to the combined activity of poly-adenylating polymerases and exosome complexes. CUT transcription occurs through RNA Polymerase II and initiates from nucleosome-depleted regions, often in an antisense orientation. To date, CUTs have a relatively uncharacterized function but have been implicated in a number of putative gene regulation and silencing pathways. Thousands of loci leading to the generation of CUTs have been described in the yeast genome. Additionally, stable uncharacterized transcripts, or SUTs, have also been detected in cells and bear many similarities to CUTs but are not degraded through the same pathways.
HOXA11-AS lncRNA is a long non-coding RNA from the antisense strand in the homeobox A. The HOX gene contains four clusters. The sense strand of the HOXA gene codes for proteins. Alternative names for HOXA11-AS lncRNA are: HOXA-AS5, HOXA11S, HOXA11-AS1, HOXA11AS, or NCRNA00076. This gene is 3,885 nucleotides long and resides at chromosome 7 (7p15.2) and is transcribed from an independent gene promoter. Being a lncRNA, it is longer than 200 nucleotides in length, in contrast to regular non-coding RNAs.
Enhancer RNAs (eRNAs) represent a class of relatively long non-coding RNA molecules transcribed from the DNA sequence of enhancer regions. They were first detected in 2010 through the use of genome-wide techniques such as RNA-seq and ChIP-seq. eRNAs can be subdivided into two main classes: 1D eRNAs and 2D eRNAs, which differ primarily in terms of their size, polyadenylation state, and transcriptional directionality. The expression of a given eRNA correlates with the activity of its corresponding enhancer in target genes. Increasing evidence suggests that eRNAs actively play a role in transcriptional regulation in cis and in trans, and while their mechanisms of action remain unclear, a few models have been proposed.
Short interspersed nuclear elements (SINEs) are non-autonomous, non-coding transposable elements (TEs) that are about 100 to 700 base pairs in length. They are a class of retrotransposons, DNA elements that amplify themselves throughout eukaryotic genomes, often through RNA intermediates. SINEs compose about 13% of the mammalian genome.
Brain cytoplasmic 200 long-noncoding RNA is a 200 nucleotide RNA transcript found predominantly in the brain with a primary function of regulating translation by inhibiting its initiation. As a long non-coding RNA, it belongs to a family of RNA transcripts that are not translated into protein (ncRNAs). Of these ncRNAs, lncRNAs are transcripts of 200 nucleotides or longer and are almost three times more prevalent than protein-coding genes. Nevertheless, only a few of the almost 60,000 lncRNAs have been characterized, and little is known about their diverse functions. BC200 is one lncRNA that has given insight into their specific role in translation regulation, and implications in various forms of cancer as well as Alzheimer's disease.
Small nucleolar RNA host gene 1 is a non-protein coding RNA that in humans is encoded by the SNHG1 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.
This database is a comprehensive mammalian noncoding RNA database (RNAdb)