Question
Describe and give the results of an experiment that shows that DNA looping is involved in the enhancement of the E. coli glnA locus.
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The goal is to demonstrate that DNA looping is involved in the enhancement of the E. coli glnA locus, which encodes glutamine synthetase and is regulated by nitrogen availability. Show more…
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When enhancers were initially found to influence transcription many thousands of nucleotide pairs from the promoters they control, two principal models were invoked to explain this action at a distance. In the "DNA looping" model, direct interactions between proteins bound at enhancers and promoters were proposed to stimulate transcription initiation. In the "scanning" or "entry-site" model, RNA polymerase (or another component of the transcription machinery) was proposed to bind at the enhancer and then scan along the DNA until it reached the promoter. These two models were tested using an enhancer on one piece of DNA and a $eta$ -globin gene and promoter on a separate piece of DNA. The $eta$ -globin gene was not expressed from the mixture of pieces. However, when the two segments of DNA were joined via a linker (made of a protein that binds to a small molecule called biotin), the $eta$ -globin gene was expressed. Does this experiment distinguish between the DNA looping model and the scanning model? Explain your answer.
When enhancers were initially found to influence transcription from many thousands of nucleotide pairs away from the promoters they control, two principal models were invoked to explain this action at a distance. In the "DNA looping" model, direct interactions between proteins bound at enhancers and promoters were proposed to stimulate transcription initiation. In the "scanning" or "entry-site" model, RNA polymerase (or another component of the transcription machinery) was proposed to bind at the enhancer and then scan along the DNA until it reached the promoter. These two models were tested using an enhancer on one piece of DNA and a $\beta$ -globin gene and promoter on a separate piece of DNA (Figure $\mathrm{Q} 8-9$ ). The $\beta$ -globin gene was not expressed when these two separate pieces of DNA were introduced together. However, when the two segments of DNA were joined via a linker (made of a protein that binds to a small molecule called biotin), the $\beta$ -globin gene was expressed. Does this experiment distinguish between the DNA looping model and the scanning model? Explain your answer.
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