Improved plasmids containing the Escherichia coli dam gene under the control of the tac promoter

Abstract We report the construction of a series of plasmids containing the dam gene under the control of the tac promoter. Cells containing these plasmids produce about 8 to 10-fold more Dam methyltransferase (Mtase) than the previously used plasmid pTP166 and avoid the use of a high temperature step necessary for the expression of Dam Mtase in the plasmid pDOX1 and thus allow its use for the study of thermosensitive mutants.