Error-prone repair induced by mutant DNA methyltransferases.

Organisms utilise cytosine-5 DNA methylation to expand their repertoire of genetic transactions. Structural studies of DNA cytosine-5 methyltransferase have revealed that DNA methyltransferases incorporate nucleotide flipping into their catalytic cycle in order to access the otherwise buried pyrimidine ring from within duplex DNA. Interestingly, substituting the catalytic nucleophile Cys with Gly can produce cytotoxic forms of the bacterial methyltransferases and cause rearrangements in the DNA. In this study the generality of the cytotoxic effect has been studied on both mono and multi-specific methyltransferases. The effect of dimerisation of methyltransferases on the rearrangement event and the specificity of DNA damage have been defined. The involvement of two DNA repair proteins RecA and UmuDC has been studied. The wild type and mutant multispecific methyltransferase (M.SPRI) has been transcribed and translated in vitro and the proteins studied using surface plasmon resonance technique. The experiments described here demonstrate for the first time how a high affinity, catalytically deficient DNA methyltransferase induces error-prone deletions in E.coli.