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 (KMnO_4). The elongation structure in vivo was similar to that of transcription complexes made in vitro with some differences. The observed reactivity to KMnO_4 of the DNA template strand was consistent with the existence of an RNA-DNA hybrid of about 12 nucleotides.