Abortive termination of bioBFCD R the bioABFCD operon of Escherichic

The nature of divergent transcription from the bioABFCD gene cluster of Escherichia coli K-12 has been studied in vitro by using DNA restriction fragments as templates. The in vitro RNA transcript initiated at the promoter pA was found to be similar to the in vivo bioA transcript, whereas the transcription initiated at PB produced a small piece of RNA less than 200 nu- cleotides long. Substituting ITP for GTP or using an S 100 cell-free extract as a source of antiterminator permitted transcription of the bioBFCD gene cluster initiating at the promoter PB to be read through. The possible site for in vitro transcription termination in the bioB region is discussed.