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Homework answers / question archive / In 2013, Randy Schekman, Thomas Siidhof
In 2013, Randy Schekman, Thomas Siidhof. and James Rothman were awarded the Nobel prize in Physiology or Medicine for discovering the machinery that regulates how cells transport maior molecules. While the ?eld of cellular transport and endomembrane system is quite complex, some of the original experiments carried out by the Nobel Laureates are surprisingly simple and elegant! Back in the 1980's. Dr. Schekman worked on a yeast strain that is defective in the synthesis of histidine, an amino acid essential for yeast. The yeast can produce an enzyme called Hls4 that converts histidinol to histidine and can thus grow normally in an environment with histidinol added. 5:. The Hlsd enzyme normally does not contain any signal peptide. When an ER Import signal is added to the enzyme. the yeast fails to grow in the presence of histidinol. What does this result tell you about the importance of the localization of the enzyme for its function? [4 pm] 51). Starting with the yeast that expresses the His4 enzyme with an ER import signal, Dr. Schekman isolated a mutant that has the ability to grow when histidinol is present. He further characterized the mutant and showed that it is defective at an early stage in ER import. Why Is it that cells with a defective Eli-import apparatus can now grow on histidinol? [3 pts] 5c. While the mutant in 5b can survive in the presence of hlstldlnol, it grows very slowly compared to wildtype [normal] yeast and has a lot of other defects. Explain why a mutation in ER import leads to such poor growth In yeast.
