The Yeast Transcription Factor GAL4: A Model for Understanding Eukaryotic Transcription

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Title: The Yeast Transcription Factor GAL4: A Model for Understanding Eukaryotic Transcription
Author: O'Neal, Melissa Ann
Abstract: The 26S proteasome regulates numerous cellular pathways , including transcription , through proteolytic and non -proteolytic methods . The Kodadek and Johnston laboratories recently established a novel function for the proteasomal ATPases : the destabilization of activator -DNA complexes . This is independent of proteolysis but requires direct activator -ATPase interactions as well as ATP hydrolysis . The Gal4 mutant Gap71 , which is hyper -sensitive to destabilization from a GAL promoter , was instrumental to this discovery . Gal4 , but not Gap71 , was mono -ubiquitylated in a HeLa nuclear extract and in vivo , suggesting that mono -ubiquitylation of an activator is critical to resisting destabilization by the proteasomal ATPases . To gain a better understanding of these events , the three amino acid substitutions in the Gap71 DNA -binding domain were individually cloned and analyzed for their contributions to the function of Gal4 . The data showed that Serine 22 and Lysine 23 but not Lysine 25 were important for the efficiency of the activator . The charge at Lysine 23 was found to be important for Gal4 -based transcription and subsequent in vitro work revealed that Gal4 was not only phosphorylated at Serine 22 but that this phosphorylation event was essential for the function of the activator . Many times a phosphorylation event precedes a mono -ubiquitylation event on an activator . Knowing the kinase and ligase machinery that modifies Gal4 would permit us to further test our model . As a result , I designed selection screens in an attempt to isolate the kinase and /or ligase machinery components that modify Gal4 . While these particular enzymes were not identified , other novel genes were found to negatively affect the galactose utilization pathway , MSU1 and SPS1 . Altogether , the data demonstrated that two post -translation events , phosphorylation and mono -ubiquitylation , prevent an activator -DNA complex from being disrupted , leading to an elegant model in which the proteasomal ATPases act as an important check point in transcription .
URI: http : / /hdl .handle .net /2152 .5 /595
Date: 2009-06-18

Citation

The Yeast Transcription Factor GAL4: A Model for Understanding Eukaryotic Transcription. Graduate School of Biomedical Sciences. Available electronically from http : / /hdl .handle .net /2152 .5 /595 .

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