The TATA box (also as a TATA element or RNA polymerases and are numbered to match their Goldberg–Hogness box) at -30 nt (full sequence corresponding RNA polymerase and lettered in the is TATAAAA). This element aids in local DNA order of discovery (e.g., TFIID was the fourth GTF denaturation and sets the start point for discovered that works with RNA polymerase II). The transcription. general transcription factors along with other proteins forming specific PICs at a particular promoter poise RNA Promoter-proximal elements are required for high polymerase to begin transcription of the gene behind levels of transcription. They are further upstream from the promoter. the start site, at positions between -50 and -200. These elements generally function in either orientation. Once the PIC forms, RNA polymerase will initiate Examples include: transcription. However, the rate at which transcription initiation occurs at a particular gene depends on 2 The CAAT box, located at about -75. factors. The first factor is the number and types of The GC box, consensus sequence GGGCGG, enhancer/silencer sequence elements found in the located at about -90. promoter. These sequence elements can be from 50 nt Various combinations of core and proximal elements to over 1,000 nt in length. Enhancer/silencer elements are found near different genes. Promoter-proximal must be located in (meaning close to) to cis elements are key to understanding the rate at which promoter/coding sequence in order to effect the transcription initiation occurs and thus the level of gene expression of a gene. Some enhancer/silencer expression. sequences have been found that are as much as 1 Eukaryotic Transcription initiation requires assembly megabase (1,000,000 nt) away from the transcription of RNA polymerase II and binding of general start site (TATA box), but most are within a few transcription factors (GTFs) on the core promoter at the thousand bases or less of the TATA box. TATA box (see The second factor regulating the rate of transcript Figure 3.31) forming a (PIC). Note that the PIC is initiation is proteins that can bind to specific or sometimes referred to simply as the transcription sequence elements. are proteins that bind to enhancer initiation complex. GTFs are needed for initiation by all sequences. Activator proteins also contain
The TATA box (also as a TATA element or Goldberg–Hogness box) at -30 nt (full sequence is TATAAAA). This element aids in local DNA denaturation and sets the start point for transcription. Promoter-proximal elements are required for high levels of transcription. They are further upstream from the start site, at positions between -50 and -200. These elements generally function in either orientation. Examples include: The CAAT box, located at about -75. The GC box, consensus sequence GGGCGG, located at about -90. Various combinations of core and proximal elements are found near different genes. Promoter-proximal elements are key to understanding the rate at which transcription initiation occurs and thus the level of gene expression. Eukaryotic Transcription initiation requires assembly of RNA polymerase II and binding of general transcription factors (GTFs) on the core promoter at the TATA box (see Figure 3.31) forming a (PIC). Note that the PIC is sometimes referred to simply as the transcription initiation complex. GTFs are needed for initiation by all RNA polymerases and are numbered to match their corresponding RNA polymerase and lettered in the order of discovery (e.g., TFIID was the fourth GTF discovered that works with RNA polymerase II). The general transcription factors along with other proteins forming specific PICs at a particular promoter poise RNA polymerase to begin transcription of the gene behind the promoter. Once the PIC forms, RNA polymerase will initiate transcription. However, the rate at which transcription initiation occurs at a particular gene depends on 2 factors. The first factor is the number and types of enhancer/silencer sequence elements found in the promoter. These sequence elements can be from 50 nt to over 1,000 nt in length. Enhancer/silencer elements must be located in cis (meaning close to) to promoter/coding sequence in order to effect the expression of a gene. Some enhancer/silencer sequences have been found that are as much as 1 megabase (1,000,000 nt) away from the transcription start site (TATA box), but most are within a few thousand bases or less of the TATA box. The second factor regulating the rate of transcript initiation is proteins that can bind to specific or sequence elements. are proteins that bind to enhancer sequences. Activator proteins also contain
ch3-MolecularGenetics_1.3.docx