A bacterial methyltransferase M.EcoHK31I requires two proteins forin vitromethylation

Abstract

The genes encoding EcoHK31I restriction-modification (R-M) system were isolated from a clinically-isolated Escherichia coil strain HK31. The entire R-M system of EcoHK31 I is located in a 2.1 kb fragment. R.EcoHK31 I is an isoschizomer of Eael which recognizes and cleaves Y.I.GGCCR. M.EcoHK3ll consists of two polypeptides α and β with sizes 309 and 176 aa, respectively. Polypeptide β is encoded within an alternative reading frame of polypeptide α. All the conserved motifs in mC5-MTases can be found in polypeptide a except motif IX which is present in polypeptide β. Polypeptides α and β were separately synthesized in a 17 promoter controlled over-expression system and in vitro methylation occurred only when the two extracts were mixed and thus confirms that two polypeptides are required for methylation.