Toxic component of a type II toxin-antitoxin (TA) system. Upon expression in E.coli and M.smegmatis inhibits cell growth and colony formation. Its toxic effect is neutralized by coexpression with cognate antitoxin MazE9. Acts as an mRNA interferase, specifically cleaving between U and C in UAC sequences. May cleave its cognate antitoxin's gene (PubMed:25608501). In E.coli expression with non-cognate antitoxins VapB27 and VapB40 partially neutralizes the toxin. Forms a complex with cognate antitoxin MazE9. Mildy induced (5 to 9-fold) by oxidative and nitrosative stress, starvation, growth in the presence of isoniazid or gentamycin, strongly induced (24-fold) when grown in a non-replicating state. 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.