Expression of β‐galactosidase from a hybrid promoter: operator element in Escherichia coli

A hybrid trpPO:lacO regulatory sequence was cloned upstream of a promoterless lacZ gene and recombined onto a Λ bacteriophage. Escherichia coli lysogens representing the four possible phenotypes for lacI and trpR were constructed and the synthesis of β‐galactosidase was assayed under various growth conditions. The results illustrated that both control elements could be efficiently and independently regulated by the addition or omission of appropriate accessory molecules.