Multiple transcriptional control of the Lactococcus lactis trp Operon

The Lactococcus lactis trpEGDCFBA operon is preceded by a noncoding leader region. Transcriptional studies of the tip operon revealed three transcripts with respective sizes of 8 kb (encompassing the entire operon), 290 bases, and 160 bases (corresponding to paras of the leader region). These transcripts mast likely result from initiation at the unique P-trp promoter, transcription termination at either T1 (upstream of the trp operon) or T2 (downstream of the trp operon), and/or processing. Three parameters were shown to differentially affect the amount of these transcripts: (i) following tryptophan depletion, the amount of the S-kb transcript increases 300- to 500-fold; (ii) depletion in any amino acid increased transcription initiation about fourfold; and (iii) upon entry into stationary phase the amount of the 8-hb transcript decreases abruptly. The tryptophan-dependent transcription control is exerted through transcription antitermination.