Endrin A pesticide isomeric with dieldrin enduracidin See ramoplanin

engrailed en Drosophila gene that controls segmental polarity. It is the archetype for one of three subfamilies of homeobox-containing genes.

enhancement effect Property of higher plant photosynthesis, discovered by Robert Emerson. The quantum yield of red light (less than 680 nm) and far red light (700 nm), when shone simultaneously on a plant, is greater than the sum of the yields of the light of the two wavelengths separately. This effect provides evidence for the cooperative interaction of two photosystems in photosynthesis.

enhancer A DNA control element frequently found 5' to the start site of a gene and which, when bound by a specific transcription factor, enhances the levels of expression of the gene, although it is not sufficient alone to cause expression. Distinguished from a promoter, which is sufficient alone to cause expression of the gene when bound; in practice, the two terms merge.

enhancer trap Technique for mapping gene expression patterns, classically in Drosophila. A transposon element carrying a reporter gene (usually beta-galactosidase), linked to a very weak promoter, is induced to jump within the genome. If the P-element reinserts within the sphere of influence of promoters and enhancers of some (random) gene, then the 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.

enkephalins Natural opiate pentapeptides isolated originally from pig brain. Leu-enkephalin (YGGFL) and Met-enkephalin (YGGFM) bind particularly strongly to S-type opiate receptors.

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