Toxic component of a type II toxin-antitoxin (TA) system. Upon expression in E.coli and in M.smegmatis partially inhibits cell growth and colony formation; its toxic effect is neutralized by coexpression with cognate antitoxin MazE6. Acts as an mRNA interferase on ssRNA, cleaving between the second and third bases in the sequences CUCCU and UUCCU (PubMed:18485066). Further experiments demonstrate that it digests between the first and second bases of UCCUU, yielding a 5'-hydroxyl end; digests M.tuberculosis mRNA (in coding as well as the 5'- and 3'-UTR regions) and 23S rRNA, digests E.coli 16S rRNA both alone and in the 70S ribosome but no data for M.tuberculosis 16S rRNA cleavage was presented. 23S and 16S rRNA digestion occurs in predicted single-stranded regions, the 16S rRNA UCCUU site is in the anti-Shine-Dalgarno site and would cleave off the last 7 nucleotides (PubMed:24709835). Non-cognate antitoxins VapB27 and VapB40 partially neutralize toxicity in vivo (PubMed:20876537). Forms a complex with cognate toxin MazE6, which neutralizes the toxin. Interacts physically with non-cognate antitoxins VapB27 and VapB40 which neutralize the toxin. Following 6 weeks of nutrient starvation. Strongly induced (17 to 25-fold) by nitrosative stress, starvation, when grown in a non-replicating state, in the presence of 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.