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  Home >> Molecular Biology Dictionary >Expressed Sequence Tag EST - Exsitu Preservation

Export
To transport a compound out of a cell. a.k.a. to secrete; to excrete.

Express
To transcribe and translate a gene's message into a peptide product

Expressed sequence tag
(EST) Short cDNA sequence. So-called because it represents part of the sequence (i.e., the "tag" of a sequence) of an expressed gene.

Randomly selected, partial cDNA sequence; represents it's corresponding mRNA. dbEST is a large database of ESTs at GenBank, NCBI.

Expression
To "express" a gene is to cause it to function. A gene which encodes a protein will, when expressed, be transcribed and ­translated to produce that protein. A gene which encodes an RNA rather than a protein (for example, a rRNA gene) will produce that RNA when expressed.

Expression clone
This is a clone (plasmid in a bacteria, or maybe a I phage in bacteria) which is designed to produce a protein from the DNA insert. Mammalian genes do not function in bacteria, so to get bacterial expression from your mammalian cDNA, you would place its coding region (i.e. no introns) immediately adjacent to bacterial transcription/translation control sequences. That artificial construct (the "expression clone") will produce a pseudo-mammalian protein if put back into bacteria. Often, that protein can be recognized by antibodies raised against the authentic mammalian protein, and vice versa

Expression library
A population of different DNA molecules encoding peptides, that has been cloned into one kind of expression vector. See library.

Expression system
Combination of host and vector which provides a genetic context for making a cloned gene function, i.e., produce peptide, in the host cell

Expression vector
A cloning vector that has been constructed in such a way that, after insertion of a DNA molecule, its coding sequence is properly transcribed and the RNA is translated. The cloned gene is put under the control of a promoter sequence for the initiation of transcription, and often also has a transcription termination sequence at its end. Such promoters are termed high level; examples include PI (the leftward promoter of phage 1) and the promoter of the yeast PGK (phosphoglycerate kinase) gene.

Expressivity
Degree of expression of a trait controlled by a gene. A particular gene may show different degrees of expression in different individuals. See variable expressivity.

Ex situ conservation
A conservation method which entails the actual removal of germplasm resources (seeds, pollen, sperm, individual organisms) from the original habitat or natural environment. cf gene bank; cryobiological preservation; in situ conservation. ex situ conservation of farm animal genetic diversity In AnGR: All conservation of genetic material in vivo, but out of the environment in which it developed, and in vitro including, inter alia, the cryoconservation of semen, oocytes, embryos, cells or tissues. Note that ex situ conservation and ex situ preservation are considered here to be synonymous. (Source: FAO, 1999)   

Ex situ preservation
See ex situ conservation.
extension Single-stranded DNA region consisting of one or more nucleotides at the end of a strand of duplex DNA. a.k.a. protruding end; sticky end; overhang; cohesive end. See extension.

 
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