Characterization of mRNA interferases from Mycobacterium tuberculosis

mRNA interferases are sequence-specific endoribonucleases encoded by the toxin-antitoxin systems in the bacterial genomes. MazF from Escherichia coli has been shown to be an mRNA inter-ferase that specifically cleaves at ACA sequences in single-stranded RNAs. It has been shown that MazF induction in E. coli effectively inhibits protein synthesis leading to cell growth arrest in the quasi-dormant state. Here we have demonstrated that Mycobacterium tuberculosis contains at least seven genes encoding MazF homologues (MazF-mt1 to -mt7), four of which (MazF-mt1, -mt3, -mt4, and -mt6) caused cell growth arrest when induced in E. coli. MazF-mt1 and MazF-mt6 were purified and characterized for their mRNA interferase specificities. We showed that MazF-mt1 preferentially cleaves the era mRNA between U and A in UAC triplet sequences, whereas MazF-mt6 preferentially cleaves U-rich regions in the era mRNA both in vivo and in vitro. These results indicate that M. tuberculosis contains sequence-specific mRNA interferases, which may play a role in the persistent dormancy of this devastating pathogen in human tissues.