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E-box
An E-box (Enhancer Box) is a DNA response element found in some eukaryotes that acts as a protein-binding site and has been found to regulate gene expression in neurons, muscles, and other tissues. Its specific DNA sequence, CANNTG (where N can be any nucleotide), with a palindromic canonical sequence of CACGTG is recognized and bound by transcription factors to initiate gene transcription. Once the transcription factors bind to the promoters through the E-box, other enzymes can bind to the promoter and facilitate transcription from DNA to mRNA.
==Discovery==
The E-box was discovered in a collaboration between Susumu Tonegawa's and Walter Gilbert's laboratories in 1985 as a control element in immunoglobulin heavy-chain enhancer. They found that a region of 140 base pairs in the tissue-specific transcriptional enhancer element was sufficient for different levels of transcription enhancement in different tissues and sequences. They suggested that proteins made by specific tissues acted on these enhancers to activate sets of genes during cell differentiation.
In 1989, David Baltimore's lab discovered the first two E-box binding proteins, E12 and E47. These immunoglobulin enhancers could bind as heterodimers to proteins through bHLH domains. In 1990, another E-protein, ITF-2A (later renamed E2-2Alt) was discovered that can bind to immunoglobulin light chain enhancers. Two years later, the third E-box binding protein, HEB, was discovered by screening a cDNA library from HeLa cells. A splice-variant of the E2-2 was discovered in 1997 and was found to inhibit the promoter of a muscle-specific gene.
Since then, researchers have established that the E-box affects gene transcription in several eukaryotes and found E-box binding factors that identify E-box consensus sequences.〔Mädge B.: E-Box. In: Schwab M. (Ed.) Encyclopedia of Cancer: SpringerReference (www.springerreference.com). Springer-Verlag Berlin Heidelberg, 2009. 〕 In particular, several experiments have shown that the E-box is an integral part of the transcription-translation feedback loop that comprises the circadian clock.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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