HIGH-LEVEL EXPRESSION OF THE CLONED GENES ENCODING THE SUBUNITS OF AND INTACT DNA METHYLTRANSFERASE, M-BULLET-ECOR124

We have cloned the genes coding for the two subunits (HsdM and HsdS) o f the type-I DNA methyltransferase (MTase). M.EcoR124, into the specia lly constructed expression vector, pJ119. These subunits have been syn thesized together as an intact MTase. We have also cloned the individu al subunit-encoding genes under the control of the T7 gene 10 promoter or the lac UV5 promoter. High levels of expression have been obtained in all cases. While HsdM was found to be soluble, HsdS was insoluble. However, in the presence of the co-produced HsdM subunit, HsdS was fo und in the soluble fraction as part of an active MTase. We have partia lly purified the cloned multi-subunit enzyme and shown that it is capa ble of DNA methylation both in vivo and in vitro.