Structural and functional analysis of the engineered type I DNA methyltransferase EcoR124I_NT

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 EcoR124I_NT, 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 EcoR124I_NT, 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.