UC San Diego

ABSTRACT OF THE THESIS

Pex36, a Novel Peroxin Implicated in de novo Peroxisome Biogenesis

By

Krypton Carolino

Masters of Science in Biology University of California, San Diego, 2017 Professor Suresh Subramani, Chair

It was previously believed that peroxisomes could only form through the growth and division of pre-existing peroxisomes. In the past decade, there has been increasing evidence suggesting that peroxisomes can also form de novo. In Pichia pastoris, peroxisomal membrane proteins (PMPs) are sorted within the endoplasmic reticulum (ER) to two distinct pre-peroxisomal ER (pER) sites, from which bud two types of pre- peroxisomal vesicles (ppVs). These ppVs then fuse heterotypically to produce import-

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competent peroxisomes. Currently, only Pex3 and Pex19 are implicated in ppV budding in P. pastoris, but their exact roles are not defined. In this study, we characterized a novel P. pastoris Pex36 protein, whose loss causes cells to display a dramatic growth delay in methanol medium due to slow peroxisome biogenesis. This growth defect in methanol is enhanced with the simultaneous deletion of another peroxin, Pex25, previously implicated in peroxisome division. Using an in vitro budding assay and fluorescence microscopy of P. pastoris Δpex36 Δpex25 cells, we found that PMPs are able to sort to the pER, but are unable to bud out, suggesting that Pex36 has a role that is redundant with Pex25, in de novo peroxisomal biogenesis, specifically in ppV budding.

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