Upstream activating sequence: Difference between revisions

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

The inositol-sensitive upstream activation sequence (UAS{{sub|INO}}) has a consensus sequence 5'-CATGTGAAAT-3' and is present in the promoter regions of genes that encode enzymes of phospholipid biosynthesis. These enzymes are regulated by inositol and choline, both of which are phospholipid precursors. Within this consensus sequence, the first six bases are homologous with canonical binding motif for proteins within the bHLH or the [[basic helix-loop-helix family]] family. Studies have shown that Ino2p and Ino4p, two bHLH regulatory proteins from ''Saccharomyces cerevisiae'', bind to promoter fragments containing this element of the consensus sequence. Additional studies have been designed to explore the function of UAS{{sub|INO}} in more detail largely in part to the fact that a large number of phospholipid biosynthetic enzyme activities in the model organism ''Saccharomyces cerevisiae'' show this common pattern of expression.<ref>{{cite journal|last1=Bachhawat|first1=Nandita|last2=Ouyang|first2=Qian|last3=Henry|first3=Susan A.|title=Functional Characterization of an Inositol-sensitive Upstream Activation Sequence in Yeast: A cis-regulatory element responsible for inositol choline-mediated regulation of phospholipid biosynthesis|journal=The Journal of Biological Chemistry|date=October 20, 1995|volume=270|pages=25087-25095|doi=10.1074/jbc.270.42.25087}}</ref>

One study explored the interaction between Ino4p and Ino2p in more depth, examining the dimerization that takes place between the two prior to binding to the promoter of the ''INO''1 gene and activating transcription. By isolating 31 recessive suppressors of the ''ino''4-8 mutant of yeast and determining that 29 were of the same locus, the researchers identified the locus as ''REG1''. One allele of ''REG1'', the suppressor mutant ''sia1-1'' was capable of suppressing the inositol auxotrophy, revealing a possible pathway for the repression of inositol-sensitive upstream activating sequence-containing genes of yeast. <ref>{{cite journal|last1=Ouyang|first1=Qian|last2=Ruiz-Noriega|first2=Monica|last3=Henry|first3=Susan A.|title=The ''REG1'' Gene Product is Required for Repression of ''INO1'' and Other Inositol-Sensitive Upstream Activating Sequence-Containing Genes of Yeast|journal=Genetics|date=May 1, 1999|volume=152|issue=1|pages=89-100}}</ref>