text: For many years, the mechanism by which RNA polymerase moves along the DNA strand during abortive initiation remained elusive. It had been observed that RNA polymerase did not escape from the promoter during transcription initiation, so it was unknown how the enzyme could read the DNA strand to transcribe it without moving downstream.  Within the last decade, studies have revealed that abortive initiation involves DNA scrunching, in which RNA polymerase remains stationary while it unwinds and pulls downstream DNA into the transcription complex to pass the nucleotides through the polymerase active site, thereby transcribing the DNA without moving. This causes the unwound DNA to accumulate within the enzyme, hence the name DNA "scrunching". In abortive initiation, RNA polymerase re-winds and ejects the downstream portion of the unwound DNA, releasing the RNA, and reverting to the RNA polymerase-promoter open complex; in contrast, in productive initiation, RNA polymerase re-winds and ejects the upstream portion of the unwound DNA, breaking RNA polymerase-promoter interactions, escaping the promoter, and forming a transcription elongation complex.
  A 2006 paper that demonstrated the involvement of DNA scrunching in initial transcription proposed the idea that the stress incurred during DNA scrunching provides the driving force for both abortive initiation and productive initiation. A companion paper published the same year confirmed that detectable DNA scrunching occurs in 80% of transcription cycles, and is actually estimated to be 100%, given the limitation of the ability to detect rapid scrunching (20% of scrunches have a duration of less than 1 second).
  A 2016 paper showed that DNA scrunching also occurs before RNA synthesis during transcription start site selection.