Transcription termination at the trp operon attenuators of Escherichia coli and Salmonella typhimurium: RNA secondary structure and regulation of termination.

Transcription termination at the attenuators of the trp operons of Escherichia coli and Salmonella typhimurium was studied in vitro using DNA restriction fragments as templates. Readthrough transcription beyond the terminators occurred with 5 and 30% efficiency, respectively, in E. coli and S. typhimurium. This difference is correlated with the stability of proposed secondary structures of the respective trp leader transcripts. Secondary structure analyses of the two leader transcripts revealed a well-conserved pattern of RNA base paring. This and the possibility that trp leader RNA is translated suggest a model for regulation of transcription termination that is based on ribosome movement along the RNA and a shift between alternative RNA base-pairing configuration.