You Are Trying to Identify the Peroxisome-Targeting Sequence in the Thiolase

question 21

Essay

You are trying to identify the peroxisome-targeting sequence in the thiolase enzyme in yeast.The thiolase enzyme normally resides in the peroxisome and therefore must contain amino acid sequences that are used to target the enzyme for import into the peroxisome.To identify the targeting sequences, you create a set of hybrid genes that encode fusion proteins containing part of the thiolase protein fused to another protein, histidinol dehydrogenase (HDH).HDH is a cytosolic enzyme required for the synthesis of the amino acid histidine and cannot function if it is localized in the peroxisome.You genetically engineer a series of yeast cells to express these fusion proteins instead of their own versions of these enzymes.If the fusion proteins are imported into the peroxisome, the HDH portion of the protein cannot function and the yeast cells cannot grow on a medium lacking histidine.You obtain the results shown in Figure 15-5.
Figure 15-5
What region of the thiolase protein contains the peroxisomal targeting sequence? Explain your answer.

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