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i just begun to study such subject, i am confused about the difference between promoter, enhancer and activitor. Can someone tell me?
Promotor is part of DNA adjacent to the gene (just few nucleotides ahead of transcripted sequence), which is crucial for the transcription. No promotor = no transcription. It's the place where the RNA Pol binds.
Enhancer can be adjacent, but also far away from the transcription start (even several thousands of bases away upstream AND downstream. I think even in the gene). It's not required for the transcription, but as name suggest, it increases the speed. That's the place where transcription factors bind (although they should bind in the nearby of promotor as well.)
Should the activator be a DNA sequence? I would consider that as a protein with activating function.
Cis or trans? That's what matters.
The promoters are found in all genes that help in transcription which eventually will lead to produce proteins, the core promoter. This is a sequence of dna bases which are located upstream of about -35 bases( ie. the opposite direction of the transcription reation). They help in aid of the transcription to happen smoothly by having effective interaction with the transcription factors, thus forming a transcription complex and it also contains the RNA polymerase binding and regulatory sites necessary for transcription to happen. They usually have sequences called consensus sequence like TATA box in eukaryote or prinbow box in prokaryotes, which initiates the transcription by unwinding the DNA.
Apart from the basal promoter, there are unique upstream promoter sequences which attract other sequence-specific transcription factors and help construct the transcription complex. Different genes are thus regulated by different promoters and combinations of transcription factors even though transcription factors are shared among genes within the cell.
Enhancer DNA sequences bind transcription factors with special protein called enhancer-binding proteins which increase the rate of transcription. Enhancer sequences may be at a distance of kilobases away from the gene they influence. An enhancer complex may interact with promoter complexes by bringing the sites into direct contact, may be by formng a loop-ike stucture.
Almost they both have the same function with some exceptions.
http://uk.answers.yahoo.com/question/in ... 117AASQKGi
thanks a lot!!
Now i think i understand
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