The other study reported in Science was conducted by Ebright's laboratory in collaboration with Terence Strick's laboratory at the Institut Jacques Monod in Paris. The study by the Rutgers/Paris team used single-molecule nanomanipulation. The researchers used an instrument referred to as "magnetic tweezers" to hold, stretch and twist a single molecule of DNA having a single start site for transcription. They then read out changes in the conformation of the DNA molecule in real time as transcription occurred. The researchers showed that the molecular machine responsible for transcription unwinds adjacent DNA segments and pulls unwound DNA into itself during initial transcription ("scrunching").
In addition, the researchers showed that machine rewinds this unwound DNA when the machine leaves the start site and begins to move down the gene ("unscrunching"). Finally, the researchers showed that this process of scrunching and unscrunching occurs every time that transcription initiation occurs, indicating that the process is an obligatory part of transcription initiation.
Taken together, the two studies answer the longstanding question of how the machine acquires the energy required to break its interactions with, and leave, the start site. The machine acquires this energy by unwinding DNA and pulling unwound DNA during initial transcription. As DNA is unwound, energy is stored in the system, in the same manner, Ebright notes, as winding the rubber band of a rubber-band-powered airplane stores energy. Eventually, there is sufficient energy stored in the system that the machine is able to break its interactions with the start site, to shoot forward and, at the same instant, to rewind the unwound DNA.
Ebright stated that the publication of these findings
Source:Rutgers, the State University of New Jersey