(37)
7. Beskrive hvordan transkriptionsfaktorer og enchancere er involveret i regulæring af eukaryot transkription
Stryer, s. 794
Stryer, s. 878
Devlin, s.214-216

Transcription factors – protein molecules that bind to the DNA sequences of cis-acting elements. The cis-acting elements can be promoters or enhancers; the name is due to the fact that these sequences are on the same molecule as the gene which transcription is regulated.

The transcription factors in eukaryotes work in a different way then the σ-factor of prokaryotes. The protein binding factors bind to the specific sequence on the DNA (enhancer or promoter) and then bind the RNA polymerase. This mechanism is called recruitment.

Enhancer – DNA sequences, 20-30 nucleotides long,  that can increase the effectiveness of the promoter enormously. The position of the enhancers relative to the promoters is not fixed; it can vary substantially. Enhancers can exert their stimulatory activity over distances over several thousand base pairs. They can be located upstream, downstream and also in the middle of the transcribed gene. Enhancers can also be present on the coding or on the anti-coding DNA strand.

Enhancers function by serving as binding sites for specific regulatory proteins, which influence transcription by perturbing the local chromatin structure to expose a gene or its promoter sequence so it is more accessible to RNA polymerase II (rather then binding to RNA polymerase II themselves)

They are found in eukaryotes and their viruses.

An enhancer is only affected in specific cells – in which the appropriate regulatory proteins are expressed.  
fx.
Immunoglobulin enhancers function only in B-lymfocyttes. 

Transcription factors and other proteins that bind to regulatory sites on the DNA can be regarded as passwords that cooperatively open multiple locks, giving RNA polymerase access to specific genes. This discovery makes it possible to understand how genes are selectively expressed in eukaryotes.

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