Growth phase-dependent regulation of Vsr endonuclease may contribute to 5-methylcytosine mutational hot spots in Escherichia coli.

Using rabbit polyclonal antibodies, we have shown that the Dcm cytosine methylase of Escherichia coli is maintained at a constant level during cell growth, while Vsr endonuclease levels are growth phase dependent. Decreased production of Vsr relative to Dcm during the log phase may contribute substantially to the mutability of 5-methylcytosine.