Overproduction of the Bacillus sphaericus R modification methylase in Escherichia coli and its purification to homogeneity

A DNA fragment containing the information coding for the GGCC-specific Bacillus sphaericus R modification methylase, BspR, was inserted into plasmid vector pKK223-3 under the control of the strong and inducible tac promoter, and transformed into Escherichia coli HB101. Upon induction this strain accumulated the methylase enzyme (while cell growth was inhibited) up to several percent of total cellular protein. Homogeneous methylase could be prepared in three purification steps.