Endoribonuclease that initiates mRNA decay. Initiates the decay of all SAM-dependent riboswitches, such as yitJ riboswitch. Involved in processing of the gapA operon mRNA, it cleaves between cggR and gapA (PubMed:19193632). Is also the decay-initiating endonuclease for rpsO mRNA. Involved in degradation of type I toxin-antitoxin system bsrG/SR4 RNAs and a minor role in degradation of type I toxin-antitoxin system bsrE/SR5 degradation (PubMed:22229825, PubMed:26940229). Magnesium. Can also use manganese or zinc. Shows preference for transcripts carrying a monophosphate group at the 5' end. Homodimer (Probable). Component of a possible RNA degradosome complex composed of rny, rnjA, rnjB, pnp, pfkA and eno (PubMed:19193632) (although rnjA and rnjB's presence is unclear). Interacts with RNA helicase CshA which may also be a member of the RNA degradosome complex (PubMed:20572937). Interacts with full-length dynamin-like protein DynA (PubMed:23060960). Dispersed along membrane with a few foci at septation sites and cell poles; in the absence of dynA fewer foci are seen, in the absence of minJ no foci are seen. Has 5 domains: N-terminal transmembrane, coiled-coil, KH, HD and an unnamed conserved C-terminal domain (residues 430-520). Both the N-terminal transmembrane helix and C-terminal domain are required for protein function in vivo. Essential; depletion mutants show a significant increase in global mRNA half-life (PubMed:19779461) a decrease in at least 1 specific mRNA processing event (PubMed:19193632); in a more severe depletion experiment alteration of about 26% of transcripts was seen (PubMed:22412379). Later shown not to be essential in 4 strains, with a doubled doubling time, cells are translucent, suggesting a possible cell surface defect. 168 trpC2 cells able to grow on minimal medium. Loss of competence for plasmid transformation, 1000-fold less sporulation. Increased sensitivity to a wide range of antibiotics. Thinner cells form long curved structures of 2-3 cell lengths, cell walls are altered with looser, considerably less dense peptidoglycan. Double pnp-rny mutants grow very slowly, while rnjA-rny mutants could not be isolated (PubMed:23504012). Increased half-life of type I toxin-antitoxin system RNAs of BsrG/SR4 (PubMed:22229825). Belongs to the RNase Y family.