UC San Diego

Vital for human survival, peroxisomes are single membrane- bound organelles ubiquitously present in cells. Their role in cellular metabolism is required for certain metabolic pathways; consequently, in yeast, their biogenesis is inducible in the presence of specific nutrients. When they are no longer required by the cell, such as in starvation conditions, peroxisomes are delivered to the vacuole (equivalent to the mammalian lysosome) through a selective autophagic process known as pexophagy. Although the molecular mechanism of pexophagy has been studied in yeast, the signal transduction pathway that regulates pexophagy is poorly understood. Thus, in order to understand the signaling components involved in the pexophagy pathway, a genome-wide screen with all of the kinases and phosphatases in Saccharomyces cerevisiae was conducted with the viable deletion set of yeast mutants. The processing of thiolase-GFP, a peroxisomal matrix marker, was used to assay pexophagy. During this process, the vacuolar processing of thiolase-GFP occurs to yield stable GFP in the vacuole. Through careful analysis, a serine/ threonine mitogen-activated protein (MAP) kinase, standard name SLT2 and systematic name YHR030C, was discovered to be involved in peroxisome turnover in Saccharomyces cerevisiae. This observation has provided novel insights through which signal networking may be transduced to initiate pexophagy inside the cell