Cloning, crystallization and preliminary X‐ray diffraction analysis of an intact DNA methyltransferase of a type I restriction–modification enzyme from Vibrio vulnificus

Independently of the restriction (HsdR) subunit, the specificity (HsdS) and methylation (HsdM) subunits interact with each other, and function as a methyltransferase in type I restriction–modification systems. A single gene that combines the HsdS and HsdM subunits in Vibrio vulnificus YJ016 was expressed and purified. A crystal suitable for X‐ray diffraction was obtained from 25%( w / v ) polyethylene glycol monomethylether 5000, 0.1  M HEPES pH 8.0, 0.2  M ammonium sulfate at 291 K by hanging‐drop vapour diffusion. Diffraction data were collected to a resolution of 2.31 Å using synchrotron radiation. The crystal belonged to the primitive monoclinic space group P 2 1 , with unit‐cell parameters a = 93.25, b = 133.04, c = 121.49 Å, β = 109.7°. With four molecules in the asymmetric unit, the crystal volume per unit protein weight was 2.61 Å 3  Da −1 , corresponding to a solvent content of 53%.