Abstract
To investigate the importance of topoisomerases for transcription of the galactose induced genes, we have studied the expression of GAL1, GAL2, GAL7 and GAL10 in Saccharomyces cerevisiae cells deficient for topoisomerases I and II. We find that topoisomerases are required for transcriptional activation of the GAL genes, but are dispensable for ongoing transcription, eliminating a role of the enzymes in transcriptional elongation. Furthermore, we demonstrate that promoter chromatin remodeling of the GAL genes is unaffected in the topoisomerase deficient strain. However, the cells fail to successfully recruit RNA polymerase II due to an inability of the TATA-binding protein (TBP) to bind to the TATA box in these promoters. We therefore argue that topoisomerases are required for accurate assembly of the preinitiation complex at the promoters of the GAL genes.
Highlights
Several studies have demonstrated that transcription and DNA supercoiling are tightly coupled [1, 2]
The GAL genes are a group of genes, which is induced when galactose is used as the carbon source in S. cerevisiae
Our findings have revealed that topoisomerase activity is required for transcriptional activation of the GAL genes, whereas ongoing transcription can occur in the absence of Top1 and Top2
Summary
Several studies have demonstrated that transcription and DNA supercoiling are tightly coupled [1, 2]. The impact of transcription on DNA supercoiling has been explained by the “Twinsupercoiled-domain-model” [3], which implies that transcription by an RNA polymerase generates domains of positive and negative supercoiling in front of and behind the polymerase, respectively. These changes in superhelicity may eventually stop the advancing polymerase and/or perturb protein-DNA interactions if not removed or dispersed to other regions. Top removes helical tension by introducing a nick in one of the DNA strands, relieving superhelical tension by rotation of the cleaved strand around the intact strand. Top creates a transient double-stranded break in the DNA in order to transport another DNA duplex through
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