You have set up a cell-freetranscription system in a test tube. By mixing DNA, R

Question

You have set up a cell-freetranscription system in a test tube. By mixing DNA, RNApolymerase, sigma factors, ribonucleotides and other essentialsubstances, you are able to make mRNAs identical to those madeunder a variety of conditions in the cells from which thesecomponents were isolated. What would happen if you were ableto remove the sigma factor first added to the tube and replace itwith another sigma factor? @importurl(/webapps/wysiwyg/htmlarea/bb_htmlarea.css); .textBoxEditorText{ font-size: .9em; } .expanded { display: block; } .collapsed {display: none; } .embedded { background-color:#EEEEEE; margin:50px; padding: 50px; }

Explanation / Answer

      Sigma factor is used torecognize the promoter region on DNA to initiate the process oftranscription.       Once the process oftranscription is initiated at the promoter region by sigmafactor(70), this subunit dissociates from       the RNA polymeraseand rejoins the polymerase only after the process iscompleted.       When this sigma factor isadded to the cell free extract, it first recognizes the promoterregion unwinds it and gets       dissociated.       During the rest of theprocess it is not associated with the polymerase.       Hence, when the firstadded sigma factor is removed from the tube and is replaced withanother sigma factor the       transcription may not beinitiated.       If the second time addedsigma factor is again a 70 subunit thetranscription can be initiated.       If another is added it maynot be i nitiated which means that transcription will notoccur.

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