High-level expression of the cloned ada gene of Escherichia coli by deletion of its regulatory sequence.

The Ada protein, a methyltransferase for repair of several alkyl adducts in DNA, was expressed in its native form at a high level in Escherichia coli from a pUC9 recombinant plasmid carrying ada gene from which the sequence controlling the Ada induction was deleted. The regulatory sequence appears to act as a terminator of transcription initiated from the lac promoter of the vector. However, deletion of the regulatory sequence resulted in elimination of ada induction by alkylating agents, providing confirmation of its role in activation of ada expression.