Upstream activating sequence: Difference between revisions

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An '''upstream activation sequence''' (UAS) is a [[Cis-regulatory element|cis-acting regulatory sequence]]. It is distinct from the [[promotor (biology)|promoter]] and increases the [[Transcription (genetics)|expression]] of a neighbouring [[gene]]. Due to its essential role in activating transcription, the upstream activating sequence is often considered to be analogous to the function of the [[Enhancer (genetics)|enhancer]] in multicellular eukaryotes.<ref>{{cite journal|last1=Webster|first1=Nocholas|last2=Jin|first2=Jia Rui|last3=Green|first3=Stephen|last4=Hollis|first4=Melvyn|last5=Chambon|first5=Pierre|title=The Yeast UAS{{sub|G}} is a transciptional enhancer in human hela cells in the presence of the GAL4 trans-activator|journal=Cell|date=29 January 1988|volume=52|issue=2|pages=169–178|doi=10.1016/0092-8674(88)90505-3}}</ref> Upstream activation sequences are a crucial part of induction, enhancing the expression of the enzyme of interest through increased transcriptional activity.<ref>{{cite journal|last1=West, Jr.|first1=Robert W.|last2=Yocum|first2=R. Rogers|last3=Ptashne|first3=Mark|title=''Saccharomyces cerevisiae'' GAL1-GAL10 Divergenet Promoter Region: Location and Function of the Upstream Activating Sequence UAS{{sub|G}}|journal=Mollecular and Cellular Biology|date=November 1984|volume=4|issue=11|pages=2467–2478}}</ref> The upstream activation sequence is found adjacently upstream to a minimal promoter (TATA box) and serves as a binding site for transactivators. If the transcriptional transactivator does not bind to the UAS in the proper orientation then transcription cannot begin.<ref>{{cite journal|last1=Lewandoski|first1=Mark|title=Conditional control of gene expression in the mouse|journal=Nature Reveiws Genetics|date=October 2001|volume=2|pages=743–755|doi=10.1038/35093537}}</ref> To further understand the function of an upstream activation sequence, it is beneficial to see its role in the cascade of events that lead to transcription activation. The pathway begins when activators bind to their target at the UAS recruiting a [[mediator (coactivator)|mediator]]. A TATA-binding protein subunit of a [[transcription factor]] then binds to the [[TATA box]], recruiting additional transcription factors. The mediator then recruits [[RNA polymerase II]] to the pre-initiation complex. Once initiated, RNA polymerase II is then released from the complex and transcription begins.<ref>{{cite journal|last1=Wion|first1=Didier|last2=Casadesus|first2=Josep|title=N{{sup|6}}-methyl-adenine: An epigenetic signal for DNA-protein interactions|journal=Nature Reviews Microbiology|date=March 2006|volume=4|pages=183–192|doi=10.1038/nrmicro1350}}</ref>

==Examples of Upstream Activation Sequences==

===''GAL1-GAL10'' Intergenic Region (UAS{{sub|G}})===

The property of the ''GAL1-GAL10'' to bind the ''GAL4'' protein is utilised in the [[GAL4/UAS system|GAL4/UAS technique]] for controlled gene misexpression in Drosophila. This is the most popular form of binary expression in ''Drosophila melanogaster'', a system which has been adapted for many uses to make ''Drosophila melanogaster'' one of the most genetically tractable multicellular organisms.<ref>{{cite journal|last1=Wimmer|first1=Ernst A.|title=Applications of insect transgenesis|journal=Nature Reviews Genetics|date=March 2003|volume=4|pages=225–232|doi=10.1038/nrg1021}}</ref> In this technique, four related binding sites between the ''GAL10'' and ''GAL1'' loci in ''Saccharomyces cerevisiae'' serve as an Upstream Activating Sequences (UAS) element through ''GAL4'' binding.<ref>{{cite journal|last1=Duffy|first1=Joseph B.|title=GAL4 system in Drosophilia: A Fly Geneticist's Swiss Army Knife|journal=Genesis|date=2002|volume=34|issue=1-2|pages=1–15|doi=10.1002/gene.10150}}</ref> Several studies have been conducted with ''[[Saccharomyces cerevisiae]]'' to explore the exact function of upstream activation sequences, often focusing on the aforementioned ''GAL1-GAL10'' intergenic region [https://www.wikigenes.org/e/gene/e/852307.html].

One study explored the galactose-responsive upstream activation sequence (UAS{{sub|G}}),looking at the influence of proximity to this UAS for nucleosome positioning. Proximity to the UAS was chosen because deletions of DNA flanking the UAS left the nucleosome array unaltered, indicating that nucleosome positioning was not related to sequence-specific histone-DNA interactions. The role of specific regions of UAS{{sub|G}} was analyzed by inserting oligonucleotides with different binding properties, leading to the successful identification of a region responsible for the creation of an ordered array. It should be noted that the sequence identified overlapped a binding site for ''GAL4'' protein, which is a positive regulator for transcription which coincides with the function of upstream activating sequences.<ref>{{cite journal|last1=Fedor|first1=Martha J.|last2=Lue|first2=Neal F.|last3=Kornberg|first3=Roger D.|title=Statistical positioning of nucleosomes by specific protein-binding to an upstream activating sequence in yeast|journal=Journal of Molecular Biology|date=5 November 1988|volume=204|issue=1|pages=109–127|doi=10.1016/0022-2836(88)90603-1}}</ref>

Another study looked at the effect of inserting the UAS{{sub|G}} into the promoter region of the glyceraldehyde-3-phosphate dehydrogenase gene (GPD) [https://www.wikigenes.org/e/gene/e/174603.html]. This hybrid promoter was then utilized to express human immune interferon, a toxic substance to yeast that results in a reduced copy number and low plasmid stability. Relative to the native promoter, expression of the hybrid promoter was induced roughly 150- to 200-fold in the cultures by growth in galactose, induction that wasn't apparent with glucose as the carbon source. When compared to the native GPD promoter, the presence of UAS{{sub|G}} caused the transcriptional activity to remain equivalently enhanced under induced conditions.<ref>{{cite journal|last1=Bitter|first1=Grant A.|last2=Egan|first2=Kevin M.|title=Expression of interferon-gamma from hybrid yeast GPD promoters containing upsream regulatory sequences from the GAL1-GAL10 intergenic region|journal=Gene|date=30 September 1988|volume=69|issue=2|pages=193–207|doi=10.1016/0378-1119(88)90430-1}}</ref>

===Inositol-sensitive Upstream Activation Sequence (UAS{{sub|INO}})===