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Identification of trp-p2, an internal promoter in the tryptophan operon of Escherichia coli

1982; Elsevier BV; Volume: 156; Issue: 2 Linguagem: Inglês

10.1016/0022-2836(82)90327-8

1089-8638

Heidi Horowitz, Terry Platt,

RNA and protein synthesis mechanisms

Previous genetic studies localized an internal low efficiency promoter, called p2, within the distal portion of the D gene of the tryptophan (trp) operon of Escherichia coli. The nucleotide sequence of trpD reveals a promoter-like region about 150 nucleotides from the 3′ end of the gene. We report here the results of transcription studies in vitro that confirm the assignment of the trp-p2 promoter by demonstrating the synthesis of a discrete RNA transcript and identifying the precise startpoint of transcription. To characterize the promoter further, we cloned a fragment of DNA containing this region into a vector such that it would direct the expression of the galactokinase gene. Under these conditions, trp-p2 functions in vivo at a level of about 15% of the primary trp promoter. A comparison of the nueleotide sequence to a “consensus” promoter sequence of E. coli reveals that its efficiency is probably limited by the constraints imposed by the coincident amino acid sequence of trpD. We discuss circumstantial evidence that trp-p2 is not accidental, and may provide a bypass function advantageous to the cell under conditions of severe nutritional deprivation.