opp-lac Operon fusions and transcriptional regulation of the Escherichia coli trp-linked oligopeptide permease.

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RESUMO

The transcriptional regulation of the Escherichia coli trp-linked opp operon that encodes the oligopeptide permease was investigated by using lambda plac Mu51-generated lac operon fusions. Synthesis of beta-galactosidase by strains harboring oppA-lac, oppB-lac, and oppD-lac fusions occurred at a basal level when the fusion-containing strains were grown in minimal medium. The addition of L-leucine or L-alanine to exponentially growing, aerobic cultures or shifting the aerobic fusion-containing strains to anaerobic growth medium increased the synthesis of beta-galactosidase from all opp-lac fusions. When transcription of the opp operon was induced by L-leucine, the differential rate of beta-galactosidase synthesis from each opp-lac fusion increased 8- to 10-fold; this increased rate of lacZ expression from the opp-lac fusions resulted in a 5- to 6-fold increase in total beta-galactosidase activity after maximum expression was achieved. Importantly, when F'123 derivatives harboring independently isolated E. coli opp-lac operon fusions were introduced into E. coli and Salmonella typhimurium, the data clearly demonstrated that the E. coli opp operon was expressed identically and responded to the same transcriptional regulatory signals in both E. coli and S. typhimurium. A comparison of beta-galactosidase synthesis by E. coli strains harboring an opp-lac operon fusion and either an oppE+ locus or an oppE mutation demonstrated that the reduction in peptide transport produced by the oppE mutation does not result from a decrease in the level of opp operon transcription.

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