The discovery of mRNA interferases: implication in bacterial physiology and application to biotechnology.

Escherichia coli contains a large number of suicide or toxin genes, whose expression leads to cell growth arrest and eventual cell death. This raises intriguing questions as to why E. coli contains so many toxin genes and what are their roles in bacterial physiology. Among these, MazF has been shown to be a sequence-specific endoribonuclease, which cleaves mRNAs at ACA sequences to completely inhibit protein synthesis. MazF is therefore called mRNA interferase. A number of other mRNA interferases with different cleavage specificities have been discovered not only in E. coli, but also in other bacteria including Mycobacterium tuberculosis. Induction of MazF in the cell leads to cellular dormancy termed quasi-dormancy. In spite of complete cell growth inhibition, cells in the quasi-dormant state are fully capable of energy metabolism, amino acids and nucleic acids biosynthesis and RNA and protein synthesis. The quasi-dormancy may be implicated in cell survival under stress conditions and may play a major role in pathogenicity of M. tuberculosis. The quasi-dormant cells provide an intriguing novel biotechnological system producing only a protein of interest in a high yield. MazF causing Bak-dependent programmed cell death in mammalian cells may be used as a tool for gene therapy against cancer and AIDS. The discovery of a novel way to interfere with mRNA function by mRNA interferases opens a wide variety of avenues in basic as well as applied and clinical sciences.