7. (6 pts) You want to identify the mitochondrial-targeting sequence of enzyme X

Question

7. (6 pts) You want to identify the mitochondrial-targeting sequence of enzyme X using yeast. To identify the targeting sequences, you use recombinant DNA technology to create a set of genes that encode fusion proteins containing part of enzyme X fused to another enzyme Y, a cytosolic enzyme required for the synthesis of the amino acid lysine. You genetically engineer a series of yeast cells to express these fusion proteins instead of their own versions of these enzymes. If the fusion protein is imported into the mitochondria, the enzyme Y cannot function and the yeast cells cannot grow on a medium lacking lysine. You obtain the results shown in the figure below. The numbers above each protein indicate the amino acids from enzyme X present in the fusion protein. + indicates growth on medium lacking lysine; - indicates lack of growth on medium lacking lysine. Use the data above to identify the smallest range of amino acid numbers from enzyme X that contains the mitochondrial targeting sequence? Explain your answer.

Explanation / Answer

The region form 300 to 350 of X contains mitochondrial targeting sequence. Because the fused protein with 300 to 400 region was not able to grow in lysine deficient medium, where as region 350 to 400 resulted in lysine production since it was not imported to mitochondria, which shows that only 300 to 350 region is important for importing enzyme X to mitochondria.

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