DNA helicases open the duplex during DNA replication, repair and transcription. However, RNA polymerase II is the only member of its family with this requirement; RNA polymerases I and III and bacterial RNA polymerases open DNA without a helicase. In this report, characterization of XPB mutants indicates that its helicase activity is not used for RNA polymerase II promoter opening, which is instead driven by its ATPase activity. The mutants have parallels in σ54 bacterial transcription and this suggests a similar mode of opening DNA for both RNA polymerases, involving ATP-dependent enzyme conformational changes. Promoter escape is defective in these XPB mutants, suggesting that the XPB helicase acts as an ATP-driven motor to reorganize the tightly wrapped multiprotein eukaryotic preinitiation complex during the remodeling that precedes elongation and the coupling to RNA processing events.
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We thank D. Vargas for technical assistance and M.S. Fenton for discussions. The research was supported by grant GM49048 from the US National Institutes of Health.
The authors declare no competing financial interests.
About this article
Transcription without XPB Establishes a Unified Helicase-Independent Mechanism of Promoter Opening in Eukaryotic Gene Expression
Molecular Cell (2017)
Journal of Molecular Biology (2017)
Annual Review of Biochemistry (2016)