Mutational analysis and a structural model of methyl-directed restriction enzyme Mrr

The Mrr protein of Escherichia coli K12 is a cryptic Type IV restriction endonuclease whose activity appears to be triggered by high pressure stress. In this report we used high pressure to isolate and analyze several Mrr mutants, and generated a new structural model of the Mrr protein. The activity of a number of spontaneous and strategically constructed Mrr mutants is discussed in the light of this model, providing a first insight into the structure–function relationships of the Mrr enzyme.