The controlled formation of sequence specific DNA protein complexes is a fundamental feature of most genetic transactions. Studies of the impact of point mutations on the function of individual components, such as repressors, remains a key aspect of many systems and synthetic biology research programmes. One of the most dramatic systemic consequences of a point mutation is exhibited by the monomeric DNA methyltransferases M.HhaI and M.EcoRII, where substitution of a single, catalytic cysteine by either glycine or alanine, creates a lethal gain of function phenotype. In vivo expression of these point mutants promotes the deposition of high affinity nucleoprotein complexes that arrest replication in vivo, causing cell death. Interestingly, it appears that a systemic response to expression of these mutant enzymes is dramatically enhanced when they are expressed as synthetic dimers. A previously unreported form of “mutational rescue” appears to be triggered as a result of networked crosslinking of host cell DNA resulting from an increased valency of nucleoprotein complex formation. This finding may have significance for developing molecular interventions for the controlled regulation of genome function and for the development of novel antimicrobial and anticancer strategies.

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