While the initial cleavage of the long pre-30S precursor is performed by Ribonuclease (RNase) III, the following maturation steps, occuring directly on the pre-assembled ribosomal particle, are found to be highly dependent on the studied prokaryotic model. In Firmicutes, such as Bacillus subtilis, final maturation of the 5S rRNA-shortening of its 3 ′ and 5 ′ ends-is performed by the RNase M5, a ∼190 residue enzyme composed of 2 domains separated by a flexible linker (Figure ). While the C-terminal domain serves to anchor the enzyme on the rRNA, catalysis of the cleavage reaction is performed by the Toprim N-terminal domain, shared by other endonucleases, such as DNA type II topoisomerases and DNA repair recombination proteins RecR. M5, which acts as a monomer, is however the only Toprim domain-containing enzyme known to cleave its substrate on both sides of an RNA double stranded stem, which makes it of special interest. Previous works have suggested that the cleavage occurs in two steps, starting with the removal of the 3 ′ extension before reorganization of the complex to position the catalytic domain for cleavage of the 5 ′ end (Figure ). C. Tisné and coworkers recently provided molecular insights into this maturation process, with a cryo-EM structure of the complex between M5 and the pre-5S ribosome particle, complemented by X-ray structures of the two domains of M5. They showed that M5 binds the ribosomal particle as a monomer and that its Toprim active site is poised to coordinate two Mg 2+ ions, evidenced in a cristallographic structure of unbound M5 Nterminal domain obtained at a high Mg 2+ concentration (Figure ).