MCB 121_Post transcription mechanisms problems KEY

MCB 121_Post transcription mechanisms problems KEY - V R NA...

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V. RNA processing V-1. Where in the cell does mRNA splicing occur? The nucleus V-2. What is the relationship between an snRNA and a snRNP? An snRNA is a small nuclear RNA while a snRNP is that same RNA that is bound by its associated proteins V-3. Several mutually exclusive RNA:RNA interactions have been found to occur among various snRNAs and pre-mRNA. What likely biochemical activity mediates the transition from one type of interaction to another? RNA helicase V-4. Some splicing intermediates and products migrate aberrantly on denaturing gels containing a high percentage acrylamide. What is the reason for this? The lariat intermediate and excised intron are circular, branched products that would have an aberrant mobility on gels due to their shape. V-5. Briefly describe an experiment you could do to test if U1 interacts with the 5’ splice site through base pair interactions. Wild type and mutant versions of the pre-mRNA and U1 snRNA are cotransfected into cells. Wild type U1 promotes splicing of the wild type message but not the mutant version of the message where the 5’ splice site consensus sequence has been altered to reduce base pair interactions with U1. A mutation in U1 that restores this base pair interaction will not promote the splicing of the mutant message.
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V-6. Radiolabeled pre-mRNA has been incubated with nuclear extract and ATP to carry out an in vitro splicing reaction. Three different precursors are used. The first (1) contains a mutation that abolishes interaction of the 5’ splice site with U1, the second (2) contains all sequences sufficient to promote splicing. And the third (3) conatins a mutation at the 3’ splice site. A. (5) For letters a-e identify the name of the molecule that best describes the structure to the right: __d__ spliced product __a__ lariat intermediate __c__ unspliced precursor __b__ lariat intron __e__ free exon 1 B. (3) Indicate which step(s) of splicing, if any (i.e. step 1 only; step 1 and step 2; or no splicing) has successfully occurred using the three different precursor substrates. 1. ___no splicing_________ 2. ____Step 1 and Step 2_________ 3._____Step 1 only________ a. b. c. d. e. 1. 2. 3.
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V-7. Provide a brief statement of why each of the statements below is false: A. Addition of the 7-me G cap and loading of splicing factors occurs co-transcriptionally. Following transcription termination the transcript is exported from the nucleus and polyadenylated. Poly-adenlyation occurs in the nucleus prior to the transcript being exported B. The spliceosome cycle requires highly processive RNA helicase proteins to disrupt extensive RNA base pair interactions that occur between snRNPs, snRNPs and pre-mRNA and even RNA base pair interactions within a single snRNP.
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MCB 121_Post transcription mechanisms problems KEY - V R NA...

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