Mechanism of β-galactosidase induction in Escherichia coli

Abstract

Infection with T-even bacteriophage, removal of inducer and treatment with actinomycin D were used to arrest the induction of β- d-galactosidase in Escherichia coli. The incorporation of a radioactive amino acid into β-galactosidase was used to measure the appearance of enzyme-specific polypeptides. The formation of active enzyme in the presence of chloramphenicol was used to measure inactive enzyme precursor. The results indicate that, following addition of inducer, a period of 2 to 2.5 minutes is required for the completion of β-galactosidasespecific messenger RNA. During this period, extensive enzyme-specific polypeptide synthesis is already in progress. An inactive enzyme precursor begins to accumulate promptly after the completion of the messenger RNA, and active enzyme appears one minute later. These results indicate that the transcription of the β-galactosidase gene requires 2 to 2.5 minutes, and that translation of the unfinished messenger RNA occurs during this time. However, successful translation is not required for transcription, since β-galactosidase can be induced when polypeptide synthesis is completely blocked by puromycin. Bacteriophage T2 reduces the rate of host messenger RNA synthesis during the first minute of infection and blocks it almost completely during the second minute. In cells pre-induced for β-galactosidase the exponential decay of enzymeforming capacity follows immediately when induction is arrested by actinomycin D, but is delayed for 2 to 2.5 minutes when induction is arrested by phage infection or inducer removal. Apparently phage infection and inducer removal arrest the initiation of the synthesis of β-galactosidase-specific messenger RNA, but do not interfere with the completion of this synthesis.