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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Expressed Sequence Tags (ESTs), Extremozymes
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Exportin A protein which binds to a ‘cargo protein’ in the nucleus and transports the cargo through a nuclear pore to the cytoplasm with the help of Ran, a member of the GTPase superfamily.
Expressed Sequence Tags (ESTs) Small sequences (300-500bp) synthesised from mRNAs that can be amplified by PCR. They represent expressed regions of the genome. ESTs function as physical markers for cloning and full length sequencing of the cDNAs of expressed genes.
They can be identified by purifying mRNAs, converting to c DNAs, and sequencing a portion of the cDNAs
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Expression (gene or protein) An index of the presence, amount, and time-course of one or more gene products in a particular cell or tissue. Expression studies are carried out at the mRNA or protein level to determine the number, type, and level of genes that may be up-regulated or down-regulated during a cellular process, in response to a stimulus, or in health and disease. Gene chips and proteomics enable analysis of expression profiles of sets of genes or even entire genomes
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Expression profiling The search for genes expressed in specific tissues during normal or disease states. The techniques used for expression profiling include differential display, hybridisation based methods by blotting or gene chips, cloning methods and sequence based methods such as SAGE. Expression profiling has application in drug target identification and validation, functional genomics, diagnostic marker development, systems biology and chemical genomics.
Expression site The genetic location of an expression-linked copy of a variable surface glycoprotein. The expression sites are located near the telomeres of a chromosome.
Expression system The combination of host and vector that makes possible the production of peptides from a cloned gene in the host cell
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Expression vector A cloning vector that enables transcription and translation of a cloned gene inserted into it. The cloned gene is placed under the control of a promoter sequence for the initiation of transcription, and usually also has a transcription termination sequence at its end. Such promoters are termed high level promoters. Examples include P1 (the leftward promoter of phage l) and the promoter of the yeast PGK (phosphoglycerate kinase) gene.
Expression-linked copy (ELC) The variable surface glycoprotein gene expressed at any one time during the developmental cycle of the trypanosome.
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Expression vector A cloning vector that enables transcription and translation of a cloned gene inserted into it. The cloned gene is placed under the control of a promoter sequence for the initiation of transcription, and usually also has a transcription termination sequence at its end. Such promoters are termed high level promoters. Examples include P1 (the leftward promoter of phage l) and the promoter of the yeast PGK (phosphoglycerate kinase) gene.
Express To transcribe and translate genetic information into a peptide product.
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Expression-linked copy (ELC) The variable surface glycoprotein gene expressed at any one time during the developmental cycle of the trypanosome.
Expressivity The degree of expression of a trait controlled by a gene. A particular gene may show different levels of expression in different individuals. See variable expressivity
Expression library A population of different DNA molecules cloned into one kind of expression vector. The vector has a promoter sequence adjacent to the insertion site and gene expression in controlled by the regulatory elements of the vector.
Expression microdissection A tissue microdissection method that allows array target to be prepared from cells that express a particular protein. This involves use of a specially designed polymer linked to an antibody for cell targeting and to reverse transcriptase for subsequent labeling of cDNA in the marked cells.
Expression profile The level and duration of expression of one or more genes, selected from a particular cell or tissue type, obtained by a variety of high-throughput methods, such as sample sequencing, serial analysis, or microarray-based detection.
Expressome A term that encompasses transcripts, proteins and other ligands.
Exteins Protein fragments from a precursor protein that are ligated together after removal of inteins during protein splicing.
Extension A region of single-stranded DNA with one or more nucleotides at the end of a duplex DNA molecule. Also called sticky end, protruding end, overhang, cohesive end.
3’-Extension A short single-stranded nucleotide sequence at the 3’-hydroxyl of a DNA duplex. Also called 3’-sticky end, 3’-protruding end, 3’-overhang.
5’-Extension A short single-stranded nucleotide sequence at the 5’-phosphate end of a DNA duplex. Also called 5’-sticky end, 5’-protruding end, 5’-overhang.
External guide sequence (EGS) See guide sequence.
Extinction The irreversible stated of a species or other group of organisms of having no living representatives, following the death of the last surviving individual of that species or group. Extinction, which occurs on a local or global level can result from various human activities, including the destruction of habitats or the overexploitation of species that are hunted or harvested as a resource.
Extinction coefficient The constant of proportionality relating the molar concentration of a substance and the absorbance of its solution.
Extra chromosomes Self-replicative genetic elements that are distinct from main chromosome(s) of a cell. This definition generally excludes viruses. In bacterial, plasmids are the predominant extra chromosomes; they encode functions that are not essential for the growth and division of the host cell. In eukaryotes, extra chromosomes may be either essential or nonessential. They may be present in the nucleus (e.g., extra chromosomal rDNA, yeast 2mm plasmid); the cytosol (e.g., dsRNA molecules in fungi); or the cytoplasmic organelles (e.g., mitochondrial DNA, chloroplast DNA). Eukaryotic extrachromosomal elements may be identified genetically by their failure to segregate at meiosis.
Extracellular Outside the cell.
Extracellular fluid (ECF) The water located outside the cell. It constitutes one third of the total body water and is present in several subcompartments such as the intravascular volume and interstitial fluid.
Extracellular matrix A complex network of polysaccharides (glycosaminoglycans or cellulose) and proteins (collagen) secreted by cells. It serves as a structural element in tissues and plays a role in tissue development and function.
Extrachromosomal element A DNA molecule that is not part of the host cell chromosome.
Extrachromosomal inheritance See cytoplasmic inheritance.
Extranuclear genes Genes present outside the nucleus in organelles such as mitochondria and chloroplasts.
Extravasation A process by which leukocytes move from the circulation into the tissues.
Extremophiles Organisms that live in ‘extreme conditions’. These include thermophiles that live at high temperatures, psychrophiles that live at very cold temperatures, halophiles that can live in concentrated salt solutions, piezophiles that thrive under high pressure such as that in deep sea (38 MPa, 375 times normal atmospheric pressure), and acidophiles and alkalophiles that live in extremely acid or alkaline conditions respectively. Enzymes from extremophiles (extremozymes) are valuable because of their stability such as Taq polymerase from Thermus aquaticus, w3hich is used in PCR.
Extremozymes Enzynes obtained from extremophiles that are useful in industrial processes because of their stability. For example, Taq polymerase from Thermus aquaticus, is used in PCR because it can withstand high temperatures during the denaturation steps.
Extrinsic protein See peripheral membrance protein.
Extrusion The export of large particles or organelles by an energy-requiring process.
Ezrin A cytoskeletal element that links the transmembrane adhesion molecule ICAM-1 (intercellular adhesion molecule 1) to the actin cytoskeleton.
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