Cis-regulerende sequenties

Transcriptional regulators are proteins that bind to short, specific stretches of non-coding DNA, known as cis-regulatory sequences. These essential components for gene regulation are present throughout the genome. 

Transcription regulators can bind to cis-regulatory sequences on DNA in its double helix form. The helical form of DNA has two grooves that differ in size. The wider groove, known as the major groove, is more accessible than the smaller minor groove, resulting in most of the interactions occurring at the major groove.  

The edges of the nitrogenous bases are exposed along the grooves and are capable of hydrogen bonding and other noncovalent interactions. 

This binding of transcriptional regulators is sequence-specific; however, closely related sequences are also recognized. This association is highly stable due to the multiple non-covalent interactions involved. 

Cis-regulatory sequences can govern every aspect of gene transcription, including the inhibition or initiation of transcription, as well as the rate of transcription. 

They can be broadly classified into those that are in close proximity to the site of transcription and those that are thousands of base pairs away. The ones that are close are usually part of the promoter sequences that initiate gene transcription.

Those that are farther away can participate in either enhancing or silencing the transcription. Often the compact packing of the DNA in the chromosome causes these sequences to be spatially close to the gene that they regulate even if they are far away in the sequence. 

A combination of several cis-regulatory sequences controls the expression of most genes. Rarely, a gene will be under the control of only a single sequence.