HIGH-RESOLUTION MAPPING OF ESCHERICHIA-COLI TRANSCRIPTION ELONGATION COMPLEX IN-SITU REVEALS PROTEIN INTERACTIONS WITH THE NONTRANSCRIBED 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 ill vivo by a protein readblock at a position distal to t he promoter. The in situ probing data provide a precise picture of a c onstrained ternary complex in which the front edge of the polymerase i s located at <6 bp from the catalytic center, Furthermore, our analyse s reveal protein contacts with the non-transcribed strand within the a rrested 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.