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TATA-Binding Protein Variants that Bypass the Requirement for Mot1 In Vivo

ABSTRACT: Mot1 is an essential TATA-binding protein (TBP)-associated factor and Snf2/Swi2 ATPase that both represses and activates transcription. Biochemical and structural results support a model in which ATP binding and hydrolysis induce a conformational change in Mot1 that drives local translocation along DNA, thus removing TBP. While this activity explains transcriptional repression, it does not as easily explain Mot1-mediated transcriptional activation, and several different models have been proposed to explain how Mot1 activates transcription. To better understand the function of Mot1 in yeast cells in vivo, particularly with regard to gene activation, TBP mutants were identified that bypass the requirement for Mot1 in vivo. Although TBP has been extensively mutated and analyzed previously, this screen uncovered two novel TBP variants that are unique in their ability to bypass the requirement for Mot1. Surprisingly, in vitro analyses reveal that rather than having acquired an improved biochemical activity, one of the TBPs was defective for interaction with Pol II preinitiation complex (PIC) components and other regulators of TBP function. The other mutant was defective for DNA binding in vitro, yet was still recruited to chromatin in vivo. These results suggest that Mot1-mediated dissociation of TBP (or TBP-containing complexes) from chromatin can explain the Mot1 activation mechanism at some promoters. The results also suggest that PICs can be dynamically unstable, and that appropriate PIC instability is critical for the regulation of transcription in vivo.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE12371 | GEO | 2008/12/17

SECONDARY ACCESSION(S): PRJNA113205

REPOSITORIES: GEO

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Project description:TATA-binding protein (TBP) is central to the regulation of transcription initiation. Recruitment of TBP to target genes can be positively regulated by one of two basal transcription factor complexes: SAGA or TFIID. Negative regulation of TBP promoter association can be performed by Mot1 or the NC2 complex. Recent evidence suggest that Mot1, NC2, and TBP form a DNA-dependent protein complex. Here, we compare the functions of Mot1 and NC2beta during basal and activated transcription using the anchor-away technique for conditional nuclear depletion. Genome-wide expression analysis indicates that both proteins regulate a highly similar set of genes (r2=0.8). Upregulated genes were enriched for SAGA occupancy, while downregulated genes preferred TFIID binding. Mot1p and NC2beta depletion during heat shock resulted in a failure to downregulate gene expression after initial activation, which was accompanied by increased TBP and RNA pol II promoter occupancies. Depletion of Mot1p or NC2beta displayed preferential synthetic lethality with the TBP-interaction module of SAGA. Our results suggest that Mot1 and NC2beta cooperate in vivo to regulate TBP function, and that they are involved in maintaining basal expression levels as well as in resetting gene expression after induction by stress. In this study 3 S. cerevisiae strains were grown with and without addition of rapamycin. For each experimental factor two independent colonies were inoculated in Complete Synthetic Medium (CSM) with 2% glucose. Overnight cultures were diluted to 0.3 OD600 in 50 ml medium and grown to 1 OD600. Cultures were then grown for 60 minutes in the absence or presence of rapamycin at 1ug/ml (LC laboratories). Cells were harvested by centrifugation at 4000 rpm for 3 minutes and were frozen in liquid nitrogen. Amplified cRNA samples were labeled with either cy3 or cy5 and put on microarray together with an oppositely labeled common reference sample consisting of cRNA of untreated wildtype strain.

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TATA-Binding Protein Variants that Bypass the Requirement for Mot1 In Vivo

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