Study+Questions+Lectures+15+_+16+mRNA+processing+KEY

Study+Questions+Lectures+15+_+16+mRNA+processing+KEY -...

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Study Questions Lectures 15/16 – RNA processing and splicing Question 1 . 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), contains 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. ___ Step1 and Step 2___ 3. ___only step 1______
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Question 2 . 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 then polyadenylated. Poly-adenlyation occurs in the nucleus prior to the transcript being exported b) The first step of splicing involves the nucleophilic attack of the 2’ OH of the branch site nucleotide at the 5’ splice site to give two products: a free exon 1 terminating with a 3’ phosphate and a branched lariat structure containing the unusual 2’-5’ phosphodiester linkage involving the first nucleotide of the intron and the branch site nucleotide. The free exon 1 that follows the first step of splicing terminates in a 3’OH d) The term snRNP stands for small nuclear RNA Particle. SnRNP stands for s mall n uclear r ibon ucleo-p rotein (particle or complex) Question 3. Mark the single most correct answer to the questions below. Which of the following cannot be co-transcriptional (i. e. cannot occur on an RNA prior to termination of transcription of that RNA) for a eukaryotic nuclear gene? _________Recognition by polyadenylation factors. _________Capping. _____X___ Translation. ________Splicing. ________Intron recognition by splicing factors Which of the following is not encoded in the gene sequence and not transcribed into the pre- mRNA? ________ The AAUAAA signal for 3’ cleavage of the mRNA transcript and addition of polyA ____X____ The poly-A tail of ~150 residues ________ The branch-point A residue that is involved in the first transesterification reaction ________ The 5’ splice site GU and the 3’ splice site AG nucleotides
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Question 4. You have been gazing at the nucleotide sequences of the U2 and U6 snRNAs and notice a region of complementary sequences between the two which has not been described to date. You wonder if this potential base pairing interaction might play a role in the process of mRNA splicing. To address this problem, you make a C to G mutation in U2 (called U2CG) and
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This note was uploaded on 02/26/2012 for the course MCB 121 taught by Professor Gasser during the Winter '09 term at UC Davis.

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Study+Questions+Lectures+15+_+16+mRNA+processing+KEY -...

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