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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, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. 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. Gene expression is summarized in the central dogma of molecular biology first formulated by Francis Crick in 1958, further developed in his 1970 article, and expanded by the subsequent discoveries of reverse transcription and RNA replication.
In molecular genetics, the three prime untranslated region (3′-UTR) is the section of messenger RNA (mRNA) that immediately follows the translation termination codon. The 3′-UTR often contains regulatory regions that post-transcriptionally influence gene expression.
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.
Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature mRNA for translation. In many bacteria, the poly(A) tail promotes degradation of the mRNA. It, therefore, forms part of the larger process of gene expression.
The RNA-induced silencing complex, or RISC, is a multiprotein complex, specifically a ribonucleoprotein, which functions in gene silencing via a variety of pathways at the transcriptional and translational levels. Using single-stranded RNA (ssRNA) fragments, such as microRNA (miRNA), or double-stranded small interfering RNA (siRNA), the complex functions as a key tool in gene regulation. The single strand of RNA acts as a template for RISC to recognize complementary messenger RNA (mRNA) transcript. Once found, one of the proteins in RISC, Argonaute, activates and cleaves the mRNA. This process is called RNA interference (RNAi) and it is found in many eukaryotes; it is a key process in defense against viral infections, as it is triggered by the presence of double-stranded RNA (dsRNA).
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal DNA (rDNA) and then bound to ribosomal proteins to form small and large ribosome subunits. rRNA is the physical and mechanical factor of the ribosome that forces transfer RNA (tRNA) and messenger RNA (mRNA) to process and translate the latter into proteins. Ribosomal RNA is the predominant form of RNA found in most cells; it makes up about 80% of cellular RNA despite never being translated into proteins itself. Ribosomes are composed of approximately 60% rRNA and 40% ribosomal proteins by mass.
RNA polymerase 1 is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA, a type of RNA that accounts for over 50% of the total RNA synthesized in a cell.
RNA-binding proteins are proteins that bind to the double or single stranded RNA in cells and participate in forming ribonucleoprotein complexes. RBPs contain various structural motifs, such as RNA recognition motif (RRM), dsRNA binding domain, zinc finger and others. They are cytoplasmic and nuclear proteins. However, since most mature RNA is exported from the nucleus relatively quickly, most RBPs in the nucleus exist as complexes of protein and pre-mRNA called heterogeneous ribonucleoprotein particles (hnRNPs). RBPs have crucial roles in various cellular processes such as: cellular function, transport and localization. They especially play a major role in post-transcriptional control of RNAs, such as: splicing, polyadenylation, mRNA stabilization, mRNA localization and translation. Eukaryotic cells express diverse RBPs with unique RNA-binding activity and protein–protein interaction. According to the Eukaryotic RBP Database (EuRBPDB), there are 2961 genes encoding RBPs in humans. During evolution, the diversity of RBPs greatly increased with the increase in the number of introns. Diversity enabled eukaryotic cells to utilize RNA exons in various arrangements, giving rise to a unique RNP (ribonucleoprotein) for each RNA. Although RBPs have a crucial role in post-transcriptional regulation in gene expression, relatively few RBPs have been studied systematically.
Eukaryotic transcription is the elaborate process that eukaryotic cells use to copy genetic information stored in DNA into units of transportable complementary RNA replica. Gene transcription occurs in both eukaryotic and prokaryotic cells. Unlike prokaryotic RNA polymerase that initiates the transcription of all different types of RNA, RNA polymerase in eukaryotes comes in three variations, each translating a different type of gene. A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.
A ribonucleoprotein particle or RNP is vessicle complex formed between RNA and RNA-binding proteins (RBPs). The term RNP foci can also be used to denote intracellular compartments involved in processing of RNA transcripts.
Non-stop decay (NSD) is a cellular mechanism of mRNA surveillance to detect mRNA molecules lacking a stop codon and prevent these mRNAs from translation. The non-stop decay pathway releases ribosomes that have reached the far 3' end of an mRNA and guides the mRNA to the exosome complex, or to RNase R in bacteria for selective degradation. In contrast to Nonsense-mediated decay (NMD), polypeptides do not release from the ribosome, and thus, NSD seems to involve mRNA decay factors distinct from NMD.
ELAV-like protein 1 or HuR is a protein that in humans is encoded by the ELAVL1 gene.
Synaptotagmin-binding, cytoplasmic RNA-interacting protein (SYNCRIP), also known as heterogeneous nuclear ribonucleoprotein (hnRNP) Q or NS1-associated protein-1 (NSAP-1), is a protein that in humans is encoded by the SYNCRIP gene. As the name implies, SYNCRIP is localized predominantly in the cytoplasm. It is evolutionarily conserved across eukaryotes and participates in several cellular and disease pathways, especially in neuronal and muscular development. In humans, there are three isoforms, all of which are associated in vitro with pre-mRNAs, mRNA splicing intermediates, and mature mRNA-protein complexes, including mRNA turnover.
Double-stranded RNA-binding protein Staufen homolog 1 is a protein that in humans is encoded by the STAU1 gene.
Adenylate-uridylate-rich elements are found in the 3' untranslated region (UTR) of many messenger RNAs (mRNAs) that code for proto-oncogenes, nuclear transcription factors, and cytokines. AREs are one of the most common determinants of RNA stability in mammalian cells.
Post-transcriptional regulation is the control of gene expression at the RNA level. It occurs once the RNA polymerase has been attached to the gene's promoter and is synthesizing the nucleotide sequence. Therefore, as the name indicates, it occurs between the transcription phase and the translation phase of gene expression. These controls are critical for the regulation of many genes across human tissues. It also plays a big role in cell physiology, being implicated in pathologies such as cancer and neurodegenerative diseases.
The Epstein–Barr virus nuclear antigen 2 (EBNA-2) is one of the six EBV viral nuclear proteins expressed in latently infected B lymphocytes is a transactivator protein. EBNA2 is involved in the regulation of latent viral transcription and contributes to the immortalization of EBV infected cells. EBNA2 acts as an adapter molecule that binds to cellular sequence-specific DNA-binding proteins, JK recombination signal-binding protein (RBP-JK), and PU.1 as well as working with multiple members of the RNA polymerase II transcription complex.
RNA recognition motif, RNP-1 is a putative RNA-binding domain of about 90 amino acids that are known to bind single-stranded RNAs. It was found in many eukaryotic proteins.
The RNA-binding Proteins Database (RBPDB) is a biological database of RNA-binding protein specificities that includes experimental observations of RNA-binding sites. The experimental results included are both in vitro and in vivo from primary literature. It includes four metazoan species, which are Homo sapiens, Mus musculus, Drosophila melanogaster, and Caenorhabditis elegans. RNA-binding domains included in this database are RNA recognition motif, K homology, CCCH zinc finger, and more domains. As of 2021, the latest RBPDB release includes 1,171 RNA-binding proteins.
Jack D. Keene is a James B. Duke Professor of Molecular Genetics and Microbiology at Duke University.
References
- ↑ Bourdeau V, Ferbeyre G, Pageau M, Paquin B, Cedergren R (November 1999). "The distribution of RNA motifs in natural sequences". Nucleic Acids Res. 27 (22): 4457–67. doi:10.1093/nar/27.22.4457. PMC 148730 . PMID 10536156.
- ↑ "ELAV family" . Retrieved 30 August 2019.
- ↑ Gerber AP, Herschlag D, Brown PO (March 2004). "Extensive association of functionally and cytotopically related mRNAs with Puf family RNA-binding proteins in yeast". PLOS Biol. 2 (3): E79. doi:10.1371/journal.pbio.0020079. PMC 368173 . PMID 15024427.
- ↑ Kosmopoulou A, Vlassi M, Stavrakoudis A, Sakarellos C, Sakarellos-Daitsiotis M (July 2006). "T-cell epitopes of the La/SSB autoantigen: prediction based on the homology modeling of HLA-DQ2/DQ7 with the insulin-B peptide/HLA-DQ8 complex". J Comput Chem. 27 (9): 1033–44. doi:10.1002/jcc.20422. PMID 16639700. S2CID 10167394.
- ↑ MacKenzie JJ, Sumargo I, Taylor SA (July 2006). "A cryptic full mutation in a male with a classical fragile X phenotype". Clin. Genet. 70 (1): 39–42. doi:10.1111/j.1399-0004.2006.00634.x. PMID 16813602. S2CID 38749866.
