The Effect of Culture Medium Composition on the Localization of Peroxisomal Membrane Proteins in Yeast

Abstract

Formation and degradation of peroxisomes are not well understood, but their absence leads to serious consequences. In the study described in this thesis, 1 sought to (1) verify previous work indicating that switching from glucose-rich medium to lipid-rich medium induces peroxisome formation; (2) reveal that switching back from lipid-rich to glucose-rich medium induces peroxisome degradation; (3) test the hypothesis that Pex3p is a class II PMP that enters the peroxisome from the endoplasmic reticulum during de novo peroxisome formation; and (4) test the hypothesis that Pxalp is a class I PMP that enters the peroxisomal membrane from the cytosol. I followed the pattern of fluorescence in yeast cells expressing Pex3p-Green Fluorescent Protein (GFP) and Pxalp-GFP fusion proteins after cells were transferred either from a glucose-rich to a lipid- rich medium or vice versa. I succeeded in producing GFP transformants for two peroxisome genes. I also confirmed that switching to lipid-rich medium induced peroxisome formation and demonstrated that switching the peroxisomes back into the glucose medium triggered a rapid degradation. Evidence consistent with the hypotheses that Pex3p moves from the ER to the peroxisomal membrane and that Pxalp is transported from the cytosol to the membrane was obtained, but the overall support was weak.