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.