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In eukaryotes three major nuclear RNA Polymerases (Pols I, II and III) transcribe the genome. Pols II and III transcribe many different genes. Pol I has only one target from which it synthesizes the precursor for 3 of 4 ribosomal (r)RNAs accounting for up to 60 percent of total cellular RNA. Dedication of Pol I and its specific transcription factors to transcribe a single gene underlines the importance of rRNA synthesis. Research in Regensburg aims at understanding mechanism(s) of Pol I transcription.

Trabajo presentado al EMBO Workshop: "Gene transcription in yeast: From global analyses to single cells", celebrado en Sant Feliu de Guixols (España) del 9 al 14 de junio de 2018.

Trabajo presentado a la OddPols: International Conference on Transcription by RNA Polymerase I, III, IV and V, celebrada en Toulouse (Francia) del 26 al 29 de junio de 2018.

Eukaryotic RNA polymerase I (Pol I) is specialized in rRNA gene transcription synthesizing up to 60% of cellular RNA. High level rRNA production relies on efficient binding of initiation factors to the rRNA gene promoter and recruitment of Pol I complexes containing initiation factor Rrn3. Here, we determine the cryo-EM structure of the Pol I-Rrn3 complex at 7.5 angstrom resolution, and compare it with Rrn3-free monomeric and dimeric Pol I. We observe that Rrn3 contacts the Pol I A43/A14 stalk and subunits A190 and AC40, that association re-organizes the Rrn3 interaction interface, thereby preventing Pol I dimerization; and Rrn3-bound and monomeric Pol I differ from the dimeric enzyme in cleft opening, and localization of the A12.2 C-terminus in the active centre. Our findings thus support a dual role for Rrn3 in transcription initiation to stabilize a monomeric initiation competent Pol I and to drive pre-initiation complex formation.