Molecular Biology help thank you In the Travers and Burgess

Molecular Biology help? thank you!

In the Travers and Burgess experiment, they first concluded that sigma played a role in transcription initiation AND elongation. What was the evidence that led them to make this incorrect conclusion? In your answer, not only related the results to their conclusion, but which part of the conclusion is incorrect and what was the mistake in their interpretation.

Solution

The Travers and Burgess experiment in 1969 did a SDS-PAGE of RNA polymerase from E.coli and it showed several subunits. They found out sigma subunit which is a specificity factor and played a role in transription and elongation. The evidence was that T and B conducted an experiment to support this hypothesis. They added sigma at different concentrations and measured the rate of transcription with radioactive nucleotides. They concluded that the more sigma, the more initiation and synthesis.

They went wrong when Travers and Burgess claimed that the sigma factor is recycled. Upon promoter clearance, sigma dissociates from RNA Polymerase and joins new core to initiate another RNA chain. But Roberts et al experimet in 1996 showed that sigma is not recycled, its still attached to core at positions +16/+17 well after promoter clearance has occured. T and B experiment model involved harsh separation techniques that could strip sigma off the core if its weakly bound. so, they wrongly concluded that sigma is recyclable.

With the help of Leading edge FRET( Fluorescence Resonance Energy Transfer) Technique, it was shown that the distance between the 2 probes decreasing, showing that sigma is not released and not dissociate from the core during elongation.