Trans-dominant mutation affecting restriction and modification in Escherichia coli K-12.

We have analysed the mechanism of action of a ts mutation in E. coli, which has an effect on the expression of the restriction and modification phenotype. The frequencies of recombinants obtained in transduction experiments support the idea that the temperature sensitive mutation is located outside the hsd operon in the gene denoted hsd.X. Complementation experiments demonstrated the trans-dominant nature of the temperature sensitive mutation. The possible role of the hsd.X product in the formation of EcoR.K and EcoM.K complexes and their interaction with the recognition site on the DNA is discussed.