Toxic component of a type II toxin-antitoxin (TA) system. A sequence-specific endoribonuclease it inhibits protein synthesis by cleaving mRNA and inducing bacterial stasis. It is stable, single-strand specific with mRNA cleavage independent of the ribosome, although translation enhances cleavage for some mRNAs (PubMed:18854355). Cleavage occurs at the 5'-end of ACA sequences, yielding a 2',3'-cyclic phosphate and a free 5'-OH, although cleavage can also occur on the 3'-end of the first A (PubMed:15537630, PubMed:23280569). Digests 16S rRNA in vivo 43 nts upstream of the C-terminus; this removes the anti-Shine-Dalgarno sequence forming a mixed population of wild-type and 'stress ribosomes'. Stress ribosomes do not translate leader-containing mRNA but are proficient in translation of leaderless mRNA, which alters the protein expression profile of the cell; MazF produces some leaderless mRNA (PubMed:21944167). The toxic endoribonuclease activity is inhibited by its labile cognate antitoxin MazE. Toxicity results when the levels of MazE decrease in the cell, leading to mRNA degradation. This effect can be rescued by expression of MazE, but after 6 hours in rich medium overexpression of MazF leads to programmed cell death (PubMed:8650219, PubMed:11222603). MazF-mediated cell death occurs following a number of stress conditions in a relA-dependent fashion and only when cells are in log phase; sigma factor S (rpoS) protects stationary phase cells from MazF-killing (PubMed:15150257, PubMed:19251848). Cell growth and viability are not affected when MazF and MazE are coexpressed. Both MazE and MazE-MazF bind to the promoter region of the mazE-mazF operon to inhibit their own transcription. MazE has higher affinity for promoter DNA in the presence of MazF (PubMed:25564525). Cross-talk can occur between different TA systems, ectopic expression of this toxin induces transcription of the relBEF TA system operon with specific cleavage of the mRNA produced (PubMed:23432955). Might also serve to protect cells against bacteriophage; in the presence of MazE-MazF fewer P1 phages are produced than in a disrupted strain. For strain K38 most wild-type cells are killed but not by phage lysis; it was suggested that MazE-MazF causes P1 phage exclusion from the bacterial population. This phenomenon is strain dependent. The physiological role of this TA system is debated. Programmed cell death (PCD) occurs when cells are at high density and depends on the presence of MazE-MazF and a quorum sensing pentapeptide, the extracellular death factor (EDF) with sequence Asn-Asn-Trp-Asn-Asn (NNWNN), probably produced from the zwf gene product glucose-6-phosphate 1-dehydrogenase (PubMed:17962566, PubMed:18310334). Cell death governed by the MazE-MazF and DinJ-YafQ TA systems seems to play a role in biofilm formation, while MazE-MazF is also implicated in cell death in liquid media (PubMed:19707553). Implicated in hydroxy radical-mediated cell death induced by hydroxyurea treatment (PubMed:20005847, PubMed:23416055). In conjunction with EDF prevents apoptotic-like death (ALD) in the presence of DNA damaging agents, probably by reducing recA mRNA levels in a non-endonuclease-mediated manner (PubMed:22412352). Other studies (in strains BW25113 and MC4100, the latter makes EDF) demonstrate MazF does not cause PCD but instead bacteriostasis and possibly a dormant state as well as persister cell generation (PubMed:24375411). (Microbial infection) RNA cleavage activity is reduced when ADP-ribosylated. Inhibited by Mg(2+) (PubMed:15537630). Stimulated in vitro in a concentration-dependent fashion by EDF, which is able to overcome inhibition by cognate antitoxin MazE (PubMed:21419338). The TA system is antagonized by stress response kinase SrkA, but probably not by phosphorylation of MazF (PubMed:23416055). Probably a dimer. Forms a heterohexamer composed of alternating toxin and antitoxin homodimers MazF(2)-MazE(2)-MazF(2). The binding site of MazE and ssRNA or ssDNA are largely overlapping; the presence of only 1 MazE molecule inhibits mRNA endoribonuclease activity. Binds to EDF but not a mutated EDF (NNGNN) (PubMed:21419338). Expressed in exponentially growing cells. Induction has been reported to occur after amino acid starvation in a ppGpp-independent fashion and to be Lon protease-dependent (PubMed:12972253), but also to not occur after amino acid starvation and to be regulated by ppGpp (PubMed:8650219). Also induced in M9 minimal medium and by chloramphenicol treatment (PubMed:21944167). MazE alone and in combination with MazF, represses transcription of the mazE-mazF operon. Fis activates transcription. Part of the relA-mazE-mazF-mazG operon, there is also a second mazE-mazF specific promoter which is negatively autoregulated (PubMed:2844820, PubMed:8650219). Operon induced by ectopic expression of toxin RelE; operon induction by amino acid starvation requires the relBEF operon (PubMed:23432955). Loop 1 (residues 17-28) effects catalytic activity while recognition of the ACA cleavage site is influenced by loop 2 (residues 53-61). Alterations of loop 2 generate new cleavage sites in addition to retaining the original cleavage site. (Microbial infection) ADP-ribosylated by enterobacteria phage T4. Decreased sensitivity to dramatic intracellular increases of ppGpp. Cells missing mazE-mazF survive high temperature, various DNA-damaging agents and H(2)O(2) exposure better than wild-type cells. Cells missing mazE-mazF produce more P1 phage than wild-type cells, while introduction of lysogens into a growing non-lysogenic disruption culture is lethal (PubMed:15316771). Cells missing mazE-mazF show reduced biofilm formation, and survive antibiotic treatment in log phase better than wild-type cells (PubMed:11222603, PubMed:19707553). However lag phase cells disrupted only for mazF had a lower survival rate than wild-type cells (PubMed:24375411). Cells missing mazE-mazF survive hydroxyurea treatment better than wild-type; further disruption of relE-relB and tonB yields even better survival (PubMed:20005847). Cells missing mazE-mazF undergo an apoptotic-like death (ALD) upon DNA damage characterized by membrane depolarization and DNA fragmentation; further disruption of recA prevents membrane depolarization (PubMed:22412352). Unlike the single srkA disruption mutant, a triple srkA-mazE-mazF disruption mutant shows no hyperlethality in the presence of nalidixic acid or UV light, suggesting SrkA has a negative effect on MazF (PubMed:23416055). Can be used to produce large quantities of a single protein if the gene coding for the protein does not contain any ACA codons. Up to 90% of expressed bacterial cellular protein can be the target, which can be produced for up to 4 days. The system also works in eukaryotic cells. Belongs to the PemK/MazF family. Strain K12 / MG1655 is deficient in both production and response to EDF, unlike strains K12 / MC4100, K12 / W3110 and K12 / K38, all of which make and respond to EDF.