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CH391L/S12/ToxinAntitoxins: Difference between revisions
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==Restriction Modification Systems== | ==Restriction Modification Systems== | ||
A variant of classical TA systems are restriction modification (RM) systems. RM systems involve two genes, a restriction endonuclease and a DNA methyltransferase. Here, the endonuclease acts as the toxin by cleaving non-methylated restriction sites in the host's genome wherease the methyltransferase acts as the antitoxin by protecting the endonuclease's target sites by methylation. If the source of the RM genes are lost, such as through replacement of chromosomal genes from incoming DNA sources, then the subsequent daughter cells of such a cell would have diluted and constantly degrading amount of both RM proteins. If the concentration of the DNA methyltransferase becomes low enough, it will not be able to methylate all of the endonuclease's restriction sites, resulting in DNA cleavage and possibly cell death. | A variant of classical TA systems are restriction modification (RM) systems. RM systems involve two genes, a restriction endonuclease and a DNA methyltransferase. Here, the endonuclease acts as the toxin by cleaving non-methylated restriction sites in the host's genome wherease the methyltransferase acts as the antitoxin by protecting the endonuclease's target sites by methylation. If the source of the RM genes are lost, such as through replacement of chromosomal genes from incoming DNA sources, then the subsequent daughter cells of such a cell would have diluted and constantly degrading amount of both RM proteins. If the concentration of the DNA methyltransferase becomes low enough, it will not be able to methylate all of the endonuclease's restriction sites, resulting in DNA cleavage and possibly cell death. By expressing the methyltransferase on a plasmid, one ensures that loss of the plasmid results in cell death. | ||
=Metabolism Based Plasmid Addiction= | =Metabolism Based Plasmid Addiction= | ||
