| HIV enhancer | Cis-acting regulatory sequences in the HIV long terminal repeat (ltr) which play a major role in induction or augmentation of HIV gene expression in response to environmental stimuli such as mitogens, phorbol esters, or other viruses. The HIV enhancer is the binding site for many cellular transcription factors including the nuclear factor nf-kappa b. (12 Dec 1998) |
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| enhancer element | <molecular biology> A DNA sequence, present in the genomes of higher eukaryotes and of various animal viruses, which can increase the transcription of genes into messenger RNA. These control element frequently found 5' to the start site of a gene, when bound by a specific transcription factor, enhance the levels of expression of the gene, but are not sufficient alone to cause expression. Distinguished from a promoter, that is alone sufficient to cause expression of the gene when bound, in practice, the two terms merge. Enhancers usually can function in either orientation and at various distances from a promoter. Compare: promoter. (03 Jul 1999) |
| enhancer sequence | <molecular biology> A nucleotide sequence, located as many as several thousand base pairs away in either direction from the target gene, which enhances transcription of that gene. (14 Nov 1997) |
| enhancer trap | <molecular biology, technique> Technique for mapping gene expression patterns, classically in Drosophila. A transposon element carrying a reporter gene (usually _ galactosidase), linked to a very weak promoter, is induced to jump within the genome. If the P element re inserts within the sphere of influence of promoters and enhancers of some (random) gene, then reporter gene is also expressed in a similar tissue specific manner. Usually, many lines of flies carrying such random insertions are studied, if a line shows interesting patterns of expression, it can be possible to clone the gene of interest. (18 Nov 1997) |
| actinide elements | Those elements with atomic numbers 89 to 103, corresponding to the lanthanides in the Periodic Table. Synonym: actinide elements. Origin: actinium, first element of the series (05 Mar 2000) |
| alkaline earth elements | Those element's in the family Be, Mg, Ca, Sr, Ba, and Ra, the hydroxides of which are highly ionised and hence alkaline in water solution. (05 Mar 2000) |
| alu elements | <molecular biology> A set of closely related genetic sequences, each about 300 base pairs long, in the human genome. There are 500,000 to 600,000 copies widely dispersed among all 46 chromosomes: They act as markers for human DNA sequences, although their function in the genome is unknown. The DNA fragments containing the Alu elements are formed by digesting genomic DNA with the restriction endonuclease Alu I. (14 Nov 1997) |
| rare earth elements | Those elements with atomic numbers 57-71 which closely resemble one another chemically and were once difficult to separate from one another. Synonym: rare earth elements. Origin: Lanthanum, first element of the series (05 Mar 2000) |
| P elements | A class of transposable elements in Drosophila responsible for hybrid dysgenesis; utilised as tools for introducing genes into new locations in the genome. (05 Mar 2000) |
| copia elements | A mobile genetic element with retrovirus-like sequence organization. (05 Mar 2000) |
| short interspersed elements | Repetitive sequences of DNA of about 300 base pairs in length that occur about every 3000-5000 bp in the genome. (05 Mar 2000) |
| DNA insertion elements | Discrete transposable segments of DNA which can insert into chromosomal, phage, and plasmid DNA. Some insert at random while others are site-specific; most have not been found to exist except in the inserted state. Their insertion into a genome always produces a mutation ("insertion mutation"), and their excision frequently results in a loss of host genetic information. Types of transposable elements include is elements (insertion sequence elements), which are composed of between 700 and 1400 bases and contain no genes unrelated to insertion function and tn elements (transposon elements), which are generally larger than 1400 bases and contain genes unrelated to insertion function. The concept also includes the delta element of saccharomyces cerevisiae and the integration site. (12 Dec 1998) |
| elements | Simple substances which cannot be decomposed by chemical means. They are made up of atoms which are alike in their peripheral electronic configurations, their chemical properties, and in the number of protons in their nuclei. They may differ in the number of neutrons in their nuclei. (12 Dec 1998) |
| elements, radioactive | Chemical elements which spontaneously transmute into another element with corpuscular or electromagnetic radiation. The natural radioactive elements are all those with an atomic number above 83, and some other elements, such as potassium (atomic number 19) and rubidium (atomic number 7), which are very weakly radioactive. (12 Dec 1998) |
| trace elements | A group of chemical elements that are needed in minute quantities for the proper growth, development, and physiology of an organism. (12 Dec 1998) |