High resolution mapping of E.coli transcription elongation complex in situ reveals protein interactions with the non-transcribed strand.

We have used chemical probes and UV light to perform a high resolution mapping of an Escherichia coli transcription elongation complex that was arrested in vivo by a protein readblock at a position distal to the promoter. The in situ probing data provide a precise picture of a constrained ternary complex in which the front edge of the polymerase is located at <6 bp from the catalytic center. Furthermore, our analyses reveal protein contacts with the non-transcribed strand within the arrested ternary complex. Thus, these results contribute substantially to the emerging view of a flexible transcription elongation complex in which the non-transcribed strand is an important regulatory element.