The dynamic assembly of distinct RNA polymerase I complexes modulates rDNA transcription.

Eva Torreira, Jaime Alegrio Louro, Irene Pazos, Noelia González-Polo, David Gil-Carton, Ana Garcia Duran, Sébastien Tosi, Oriol Gallego, Olga Calvo, Carlos Fernández-Tornero

eLife 2017 Mar 06

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Cell growth requires synthesis of ribosomal RNA by RNA polymerase I (Pol I). Binding of initiation factor Rrn3 activates Pol I, fostering recruitment to ribosomal DNA promoters. This fundamental process must be precisely regulated to satisfy cell needs at any time. We present in vivo evidence that, when growth is arrested by nutrient deprivation, cells induce rapid clearance of Pol I-Rrn3 complexes, followed by the assembly of inactive Pol I homodimers. This dual repressive mechanism reverts upon nutrient addition, thus restoring cell growth. Moreover, Pol I dimers also form after inhibition of either ribosome biogenesis or protein synthesis. Our mutational analysis, based on the electron cryomicroscopy structures of monomeric Pol I alone and in complex with Rrn3, underscores the central role of subunits A43 and A14 in the regulation of differential Pol I complexes assembly and subsequent promoter association.

Citation

Eva Torreira, Jaime Alegrio Louro, Irene Pazos, Noelia González-Polo, David Gil-Carton, Ana Garcia Duran, Sébastien Tosi, Oriol Gallego, Olga Calvo, Carlos Fernández-Tornero. The dynamic assembly of distinct RNA polymerase I complexes modulates rDNA transcription. eLife. 2017 Mar 06;6