In eukaryotes, activator proteins bind to _____; generalized transcription factors bind to _____
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There are hundreds of transcription factors in a cell that each bind specifically to a particular DNA sequence motif. They are not general transcription factors that bind to every promoter complex, but are recruited to a specific sequence on the promoter of a specific gene. These transcription factors bind to the promoters of a specific set of genes. In addition to the general transcription factors, other transcription factors can bind to the promoter to regulate gene transcription. Two different genes may have the same promoter but different distal control elements, enabling differential gene expression. Activators bound to the distal control elements interact with mediator proteins and transcription factors. Each enhancer is made up of short DNA sequences called distal control elements. This releases part of the protein from the DNA to activate the transcription initiation complex and places RNA polymerase in the correct orientation to begin transcription DNA-bending protein brings the enhancer, which can be quite a distance from the gene, in contact with transcription factors and mediator proteins (Figure \(\PageIndex\): An enhancer is a DNA sequence that promotes transcription. When bound along with the transcription factors, RNA polymerase is phosphorylated. Once this complex is assembled, RNA polymerase can bind to its upstream sequence. Binding of TFIID recruits other transcription factors, including TFIIB, TFIIE, TFIIF, and TFIIH to the TATA box. To initiate transcription, a transcription factor (TFIID) is the first to bind to the TATA box. RNA polymerase binds to the transcription initiation complex, allowing transcription to occur. This box is simply a repeat of thymine and adenine dinucleotides (literally, TATA repeats). Within the promoter region, just upstream of the transcriptional start site, resides the TATA box. The purpose of the promoter is to bind transcription factors that control the initiation of transcription. Consequently, the level of control of gene expression can also differ quite dramatically between genes. The length of the promoter is gene-specific and can differ dramatically between genes. This also adds more control to the transcription process. The longer the promoter, the more available space for proteins to bind. This region can be short (only a few nucleotides in length) or quite long (hundreds of nucleotides long). The promoter region is immediately upstream of the coding sequence. Genes are organized to make the control of gene expression easier. Repressors respond to external stimuli to prevent the binding of activating transcription factors.The Promoter and the Transcription Machinery.When a DNA-bending protein binds to the enhancer, the shape of the DNA changes, which allows interactions between the activators and transcription factors to occur.Enhancers can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or thousands of nucleotides away.Transcription factors bind to the promoter region and then help recruit the appropriate polymerase to begin transcription.Practice Exam 4 B/B Section Passage 1 Question 4 Practice Exam 1 B/B Section Passage 4 Question 23 Practice Exam 1 B/B Section Passage 4 Question 20 Section Bank B/B Section Passage 8 Question 57 Official Guide B/B Section Passage 2 Question 5 Therefore, a nucleotide sequence of thousands of nucleotides away can fold over and interact with a specific promoter. Whereas DNA is generally depicted as a straight line in two dimensions, it is actually a three-dimensional object. This shape change allows the interaction between the activators bound to the enhancers and the transcription factors bound to the promoter region and the RNA polymerase to occur. When a DNA-bending protein binds to an enhancer, the shape of the DNA changes. They can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or maybe thousands of nucleotides away. Įnhancer regions are binding sequences, or sites, for transcription factors. Transcriptional repressors bind to promoter or enhancer regions and block transcription whereas the transcriptional activators promote transcription. The completed assembly of transcription factors and RNA polymerase bind to the promoter, forming a transcription pre-initiation complex. Histones, repressors and activators are examples of proteins that bind to DNA.Įukaryotes require several other proteins, called transcription factors, to first bind to the promoter region and then help recruit the appropriate polymerase. DNA binding proteins help to regulate protein production, cell growth and division, and storing DNA inside the nucleus.