The Newly Identified Yeast GRD Genes Are Required for Retention of Late-Golgi Membrane Proteins

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Abstract
Processing of A-ALP, a late-Golgi membrane protein constructed by fusing the cytosolic domain of dipeptidyl aminopeptidase A to the transmembrane and lumenal domains of alkaline phosphatase (ALP), serves as a convenient assay for loss of retention of late-Golgi membrane proteins in Saccharomyces cerevisiae. In this study, a large group of novel grd (for Golgi retention defective) yeast mutants, representing 18 complementation groups, were identified on the basis of their mislocalization of A-ALP to the vacuole, where it was proteolytically processed and thus became enzymatically activated. All of the grd mutants exhibited significant mislocalization of A-ALP, as measured by determining the kinetics of A-ALP processing and by analyzing its