Gene structure and expression of the Mbol restriction - modification system

Abstract

The genes from Moraxella bovls encoding the Mbo/ restriction - modification system were cloned and expressed In Escherlchla coll. Three open reading frames were found In the sequence containing the genes. These genes, which we named mboA, mboB, and mboC, had the same orientation In the genome. Genes mbok and mboC encoded Mbol methyltransfer-ases (named M.MboA and M.MboC) with 294 and 273 amlno acid residues, respectively. The mboB gene coded for Mbol restriction endonuclease (R.Mbol) with 280 amlno add residues. Recombinant E.coli-MBOI, which contained the whole Mbol system, overproduced R.Mbol. R.Mbol activity from E.coli-MBOI was 480-fold that of M.bovis. The amino acid sequences deduced from these genes were compared with those of other restriction-modification systems. The protein sequences of the Mbol system had 38 - 49% homology with those of the Dpnll system. © 1993 IRL Press at Oxford University Press.