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This can be important for priming the cell for a rapid response as the enhancer is already bound by a pioneer transcription factor giving it a head start towards assembling the transcription preinitiation complex. Hormone responses are often quickly induced in the cell using this priming method such as with the estrogen receptor. [10]
DnaA is a protein that activates initiation of DNA replication in bacteria. [1] Based on the Replicon Model, a positively active initiator molecule contacts with a particular spot on a circular chromosome called the replicator to start DNA replication. [2] It is a replication initiation factor which promotes the unwinding of DNA at oriC. [1]
Electroporation of DNA, RNA, or ribonucleocomplexes is a common technique, though it can result in harmful effects on the target cells. [79] Chemical transfection techniques utilizing lipids and peptides have also been used to introduce sgRNAs in complex with Cas9 into cells. [80] [81] Nanoparticle-based delivery has also been used for ...
The DNA sequence that a transcription factor binds to is called a transcription factor-binding site or response element. [62] Transcription factors interact with their binding sites using a combination of electrostatic (of which hydrogen bonds are a special case) and Van der Waals forces. Due to the nature of these chemical interactions, most ...
An enhancer localized in a DNA region distant from the promoter of a gene can have a very large effect on gene expression, with some genes undergoing up to 100-fold increased expression due to an activated enhancer. [32] Enhancers are regions of the genome that are major gene-regulatory elements.
DNA can be twisted like a rope in a process called DNA supercoiling. With DNA in its "relaxed" state, a strand usually circles the axis of the double helix once every 10.4 base pairs, but if the DNA is twisted the strands become more tightly or more loosely wound. [ 43 ]
Deacetylation performed by HDAC molecules has the opposite effect. By deacetylating the histone tails, the DNA becomes more tightly wrapped around the histone cores, making it harder for transcription factors to bind to the DNA. This leads to decreased levels of gene expression and is known as gene silencing. [5] [6] [7]
Positive feedback loops like these can cause DNA methylation activity to spread out from the intended methylated target sites into genes or other regulatory elements, which can negatively affect gene expression. To prevent this spreading, DNA methylation pathways are opposed by passive and active DNA demethylation.