Reiterative transcription initiation from galP2 promoter of Escherichia coli

The expression of gal operon in Escherichia coli is driven by two promoters , P1 and P2 separated by 5 bp. The transcription initiated from the P2 gene rates a large amount of abortive transcripts to produce a comparable amount of full-length transcript as P1 in vitro. In this study, we investigated t he source of the abortive transcripts by employing a quantitative potassium permanganate footprinting method that determines the extent of open promot er complex formation. The extents of open promoter complex formation at the two gal promoters were about the same during the given reaction time while the amount of transcription initiation determined by in vitro transcriptio n assay showed a considerable difference: several hundred-fold more transcr iption initiation from the P2 than the P1, most of which was abortive. Thus , it was concluded that the abortive transcripts are generated reiterativel y by a small fraction of RNA polymerase. An in vitro transcription assay us ing an immobilized DNA template revealed that the fraction of RNA polymeras e generating abortive transcripts never produces the full-length transcript and it remains bound to the promoter. We concluded that there are two kind s of RNA polymerase-promoter complexes formed at galP2, at least in vitro, productive complex and nonproductive complex; and, the nonproductive comple x is responsible for generating large amount of abortive transcripts from t he P2. (C) 2000 Elsevier Science B.V. All rights reserved.