gen511exam3key-08

gen511exam3key-08 - 1 Genetics 511, Exam 3: 11 April 2008...

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Genetics 511, Exam 3: 11 April 2008 Name: _________________________________________ Question 1. _________ (20) 2. _________ (20) 3. _________ (20) 4. _________ (20) 5. _________ (20) __________ Total (100) 1 1
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1. Briefly describe one piece of evidence for each of the following statements (answer any 4, 5 points each. Use diagrams when appropriate): a. Some trypanosomal genes are trans-spliced. mRNA and genome sequences do not match; mRNAs contain a 35 nt leader that is not encoded in the gene. Also, treatment of splicing intermediates with de-branching enzyme yields a half-intron that is predicted to be released from a Y-shaped RNA that should be an intermediate in trans-splicing (Weaver 16.12). b. The first stage of polyadenylation is dependent on the presence of a polyA signal. Mutation of the AAUAAA blocks the first stage of polyadenylation (Weaver Figure 15.21). c. The second stage of polyadenylation does not require a polyA signal. Mutation of the AAUAAA does not block the second stage of polyadenylation (Weaver Figure 15.21). d. CPSF can bind to the polyA signal in mRNA. Gel mobility shift assay shows that CPSF can bind to RNA containing AAUAAA, but not to RNA containing AAGAAA (Weaver Figure 15.22). e. RNAi can induce methylation of gene promoter sequences. Silencing RNA targeted to promoter sequences results in promoter methylation, which can be detected as inability to be cut by a methylation-sensitive restriction enzyme. This causes a difference in the ability to PCR the promoter sequence (if methylated, DNA does not cut, and therefore can be amplified by PCR; if not methylated, DNA does cut and therefore can’t be amplified by PCR using flanking primers.). f. A 5’ cap can promote splicing of the first intron in an mRNA. In vitro splicing reactions show that a 5’ cap stimulates splicing of the first intron, but does not affect splicing of the second intron (Weaver Figure 15.30). 2. (20 points ). Answer one question (a or b). 2 2
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a. Draw the lariat model of splicing of nuclear mRNA introns, showing the interactions of the RNA transcript with the U1, U2, U4, U5 and U6 snRNAs. Answer: See sketch handed out in class; or Weaver 14.17, 14.22a. b. Describe the similarities and differences between splicing Nuclear RNA introns, Group II introns, and Group I introns. First step of splicing:
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gen511exam3key-08 - 1 Genetics 511, Exam 3: 11 April 2008...

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