Structures of B. subtilis Maturation RNases Captured on 50S Ribosome with Pre-rRNAs.

Oerum, Stephanie; Dendooven, Tom; Catala, Marjorie; Gilet, Laetitia; Dégut, Clément; Trinquier, Aude; Bourguet, Maxime; Barraud, Pierre; Cianferani, Sarah; Luisi, Ben F; Condon, Ciarán; Tisné, Carine

The pathways for ribosomal RNA (rRNA) maturation diverge greatly among the domains of life. In the Gram-positive model bacterium, Bacillus subtilis, the final maturation steps of the two large ribosomal subunit (50S) rRNAs, 23S and 5S pre-rRNAs, are catalyzed by the double-strand specific ribonucleases (RNases) Mini-RNase III and RNase M5, respectively. Here we present a protocol that allowed us to solve the 3.0 and 3.1 Ã… resolution cryoelectron microscopy structures of these RNases poised to cleave their pre-rRNA substrates within the B. subtilis 50S particle. These data provide the first structural insights into rRNA maturation in bacteria by revealing how these RNases recognize and process double-stranded pre-rRNA. Our structures further uncover how specific ribosomal proteins act as chaperones to correctly fold the pre-rRNA substrates and, for Mini-III, anchor the RNase to the ribosome. These r-proteins thereby serve a quality-control function in the process from accurate ribosome assembly to rRNA processing.