Toxic component of a type II toxin-antitoxin (TA) system. Acts as an mRNA and 23S rRNA interferase, cleaving predominantly after the first 2 Us in the sequence 5'-UUCCU-3'; in 23S rRNA only cleaves once in the ribosomal A site in dissociated but not intact ribosomes. Cleavage of 23S rRNA inhibits protein translation; the 23S rRNA region cleaved is involved in tRNA-binding in the A site, 30S and 50S subunit interaction and ribosome recycling factor association (PubMed:23650345). Upon expression in E.coli and M.smegmatis inhibits cell growth and colony formation. It dramatically increases persister cell formation in M.smegmatis upon challenge with gentamicin or kanamycin. Overexpression leads to bacteriostasis rather than bacteriocide. Its toxic effect is neutralized by coexpression with cognate antitoxin MazE3. Digests 23S rRNA in the absence of Mg(2+), increasing Mg(2+) concentrations decrease its efficiency. Forms a complex with cognate antitoxin MazE3, possibly with 1:1 stoichiometry. Mildly induced (5 to 9-fold) by starvation, when grown in a non-replicating state, in the presence of isoniazid, gentamycin or rifampicin. Individual deletion of mazF3, mazF6 and mazF9 have little to no phenotype, but a triple mutant shows increased sensitivity to oxidative and antibiotic stress and starvation, decreased formation of persisters cells, and a decreased bacterial load and pathogenic damage in infected guinea pigs. Belongs to the PemK/MazF family.