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Unformatted text preview: Name MCB121, Page 1 of 13 Last, First Burgess, Gasser MCB121-01, Winter, 2008 Final Exam, March 19, 2008 Instructions: There are thirteen pages in this exam including the cover sheet, please count them before you start to make sure all are present. Write your name on each page of the exam. Write your answers in the space provided below each question. If you need more space use the back of the page and indicate clearly that you have continued your answer on the back. Do not use additional paper. Amino acid Abbreviations Amino acid Abbreviations Alanine Ala A Leucine Leu L Arginine Arg R Lysine Lys K Asparagine Asn N Methionine Met M Aspartic acid Asp D Phenylalanine Phe F Cysteine Cys C Proline Pro P Glutamine Gln Q Serine Ser S Glutamic Acid Glu E Threonine Thr T Glycine Gly G Tryptophan Trp W Histidine His H Tyrosine Tyr Y Isoleucine Ile I Valine Val V Question Value Score 1 16 2 20 3 27 4 12 5 18 6 12 7 12 8 10 9 18 10 12 11 19 12 14 13 10 Total 200 Note: W09 we covered alternative splicing and DSB repair after MTII. So, expect the W09 final will be weighted to assign more points to those topics. Name MCB121, Page 2 of 13 Last, First Burgess, Gasser 1. (16) Sic1 is a protein that is involved in regulation of progression through the cell cycle in yeast. The rate of transcription of the Sic1 gene does not vary during the cell cycle, but the level of Sic1 protein drops dramatically at the start of the G1 stage of the cell cycle. Sic1 is a target for phosphorylation by a protein called G1 cyclin. The level of this G1 cyclin varies during the cell cycle. Phosphorylated Sic1 is a target for ubiquitation by the E3 ubiquitin ligase, SCF CDC4 . Ubiquitination targets Sic1 for degredation by the proteasome. Assuming that the following changes do not affect yeast viability, what effect would each of the following be likely to have on the level of Sic1 in the cell at the start of the G1 stage of the cell cycle. Circle I for increase in level, D for decrease in level or N for no alteration from the wild-type levels. I D N A mutation that leads to overexpression of the G1 cyclin. (more phosphorylation of Sic1 = more degradation) I D N A mutation in SCF CDC4 that makes it able to add only a single ubiquitin to each Sic1 protein. (monoubiquitinated proteins are not targeted to the proteasome) I D N A mutation replacing the lysine residue in Sic1 to which ubiquitin is normally attached, with an alanine residue. (cannot attach ubiquitin to alanine) I D N Addition of the compound MG-132, a potent inhibitor of the protease activity of the proteasome. (would inhibit degradation of Sic1) 2. (20) For each of the following, put an X in the blank next to the one correct answer to each question....
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