To the right is a DNase I foot printing experiment with a fragment of the Lac op

Question

To the right is a DNase I foot printing experiment with a fragment of the Lac operon core promoter region in the presence of RNA polymerase/sigma factor and/or the lac repressor (+ means present, - means absent). The arrow indicates the transcription initiation site. On the LEFT side of the gel, indicate the DNA regions where the proteins interact. Based on the data shown, do RNA polymerase/sigma factor and the lac repressor affect each other's binding? Explain why. For the last lane, sketch in the box the results that you predict when lactose is included in the assay. Explain your reasoning

Explanation / Answer

The lac-repressor protects the operator by bringing in some small modifications.Studies have shown that the RNA polymerase molecule asymmetrically binds to the promoter DNA and RNA polymerase protects the sequence of DNA upto a few bases of CAP-binding site,that shows that there is a direct interaction between both two.This interaction is examined using a method for direct visualization of the DNA region that is protected by protiens from DNAase attack.

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