Abstract
Transcription initiation by RNA Polymerase I (Pol I) depends on the Core Factor (CF) complex to recognize the upstream promoter and assemble into a Pre-Initiation Complex (PIC). Here, we solve a structure of Saccharomyces cerevisiae Pol I-CF-DNA to 3.8 Å resolution using single-particle cryo-electron microscopy. The structure reveals a bipartite architecture of Core Factor and its recognition of the promoter from -27 to -16. Core Factor's intrinsic mobility correlates well with different conformational states of the Pol I cleft, in addition to the stabilization of either Rrn7 N-terminal domain near Pol I wall or the tandem winged helix domain of A49 at a partially overlapping location. Comparison of the three states in this study with the Pol II system suggests that a ratchet motion of the Core Factor-DNA sub-complex at upstream facilitates promoter melting in an ATP-independent manner, distinct from a DNA translocase actively threading the downstream DNA in the Pol II PIC.
Highlights
Eukaryotic RNA synthesis is catalyzed by at least three classes of RNA Polymerases (Pol I-III) (Roeder and Rutter, 1969)
Yeast Polymerase I (Pol I) transcription initiation is regulated by four general transcription factors: the regulatory factor Rrn3, the Core Factor (CF), the TATA-box Binding Protein (TBP), and the Upstream Activation Factor (UAF) (Schneider, 2012)
Engagement of upstream promoter DNA with general transcription factors is an essential step during transcription initiation
Summary
Eukaryotic RNA synthesis is catalyzed by at least three classes of RNA Polymerases (Pol I-III) (Roeder and Rutter, 1969). Rrn association stabilizes Pol I in its monomeric and initiation-competent form (Blattner et al, 2011; Engel et al, 2016; Pilsl et al, 2016; Torreira et al, 2017), with which Core Factor further engages to facilitate Pre-Initiation Complex assembly and transcription initiation (Aprikian et al, 2001; Knutson and Hahn, 2013; Milkereit and Tschochner, 1998; Peyroche et al, 2000; Schneider, 2012).
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