Structure of transcription elongation complexes in vivo.

The opening of duplex DNA in the elongation phase of transcription by Escherichia coli RNA polymerase in vivo was detected at a regulatory site where a prolonged pause in transcription occurs. Single-stranded DNA in the transcription bubble was identified by its reactivity with potassium permanganate (KMnO4). The elongation structure in vivo was similar to that of transcription complexes made in vitro with some differences. The observed reactivity to KMnO4 of the DNA template strand was consistent with the existence of an RNA-DNA hybrid of about 12 nucleotides.