Structural and Functional Analysis of the Engineered Type I DNA Methyltransferase EcoR124INT

The Type I R–M system EcoR124I is encoded by three genes. HsdM is responsible for modification (DNA methylation), HsdS for DNA sequence specificity and HsdR for restriction endonuclease activity. The trimeric methyltransferase (M2S) recognises the asymmetric sequence (GAAN6RTCG). An engineered R–M system, denoted EcoR124INT, has two copies of the N-terminal domain of the HsdS subunit of EcoR124I, instead of a single S subunit with two domains, and recognises the symmetrical sequence GAAN7TTC. We investigate the methyltransferase activity of EcoR124INT, characterise the enzyme and its subunits by analytical ultracentrifugation and obtain low-resolution structural models from small-angle neutron scattering experiments using contrast variation and selective deuteration of subunits.