What is a helix-turn-helix transcriptional regulator?
The helix-turn-helix (HTH) domain is a common denominator in basal and specific transcription factors from the three super-kingdoms of life. At its core, the domain comprises of an open tri-helical bundle, which typically binds DNA with the 3rd helix.
What is the difference between helix loop helix and helix-turn-helix?
The key difference between helix-loop-helix and helix-turn-helix is that helix-loop-helix mediates protein dimerization, whereas helix-turn-helix regulates gene expression through DNA binding. HLH is a protein structural motif that defines one of the largest families of dimerizing transcription factors.
Why is a helix-turn-helix stable?
The first α-helical motif lies across the major groove of DNA making hydrophobic interactions with the second helix, known as the recognition helix, which lies partly within the major groove and makes specific contact with DNA. The proteins are held in a stable ordered manner by an extensive array of hydrogen bonds.
What are the zinc finger and helix-turn-helix proteins?
Four distinct structural motifs have been proposed for the DNA-binding domains of eukaryotic transcriptional regulatory proteins; the helix-turn-helix, two kinds of zinc finger, and the leucine zipper.
How do helix-turn-helix proteins bind to DNA?
It binds to the major groove of DNA through a series of hydrogen bonds and various Van der Waals interactions with exposed bases. The other α helix stabilizes the interaction between protein and DNA, but does not play a particularly strong role in its recognition.
Which are the DNA binding protein containing the helix-turn-helix structure?
Many known DNA-binding proteins have been observed to bind DNA by a number of distinct structural motifs, such as the helix–turn–helix (HTH) motif, the helix–loop–helix motif, the helix–hairpin–helix motif and the zinc finger motif (6).
How do DNA binding proteins bind to DNA?
Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes, this structure involves DNA binding to a complex of small basic proteins called histones. In prokaryotes, multiple types of proteins are involved.
How do proteins bind to specific DNA sequences?
Proteins recognize a particular sequence by having a surface that is chemically complementary to that of the DNA, forming a series of favorable electrostatic and van der Waals interactions between the protein and the base pairs.
Where is helix-turn-helix found?
The helix-turn-helix (HTH) motif is commonly found in proteins that bind DNA, especially transcription factors. In recognizing DNA, the last helix of the HTH motif that is commonly referred to as the recognition helix inserts into the DNA major groove to mediate base-specific DNA recognition.
What does the repressor bind to?
Definition. A repressor, as related to genomics, is a protein that inhibits the expression of one or more genes. The repressor protein works by binding to the promoter region of the gene(s), which prevents the production of messenger RNA (mRNA).
Are transcription factors DNA-binding proteins?
transcription factor / transcription factors One distinct feature of transcription factors is that they have DNA-binding domains that give them the ability to bind to specific sequences of DNA called enhancer or promoter sequences.
Where do transcriptional repressors bind?
How does repressor protein prevent transcription?
transcription. …“operators” where specialized proteins called repressors bind to the DNA just upstream of the start point of transcription and prevent access to the DNA by RNA polymerase. These repressor proteins thus prevent transcription of the gene by physically blocking the action of the RNA polymerase.
Is a repressor a transcription factor?
Repressors. Other transcription factors repress transcription. This repression can work in a variety of ways. As one example, a repressor may get in the way of the basal transcription factors or RNA polymerase, making it so they can’t bind to the promoter or begin transcription.
How do transcription factors bind to DNA?
The DNA sequence that a transcription factor binds to is called a transcription factor-binding site or response element. 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.
What are the three DNA-binding structures?
We focus on three structural motifs: helix–turn-helix (HTH), helix–hairpin–helix (HhH) and helix–loop–helix (HLH).
What do repressor proteins bind to?
The repressor protein works by binding to the promoter region of the gene(s), which prevents the production of messenger RNA (mRNA). Repressor proteins are essential for the regulation of gene expression in cells.
Do repressors bind to DNA?
In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.
What will happen when the repressor protein binds to the operator?
The repressor binds to the operator gene and prevents it from initiating the synthesis of the protein called for by the operon. The presence or absence of certain repressor molecules determines whether the operon is off or on.