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J. Cell Biol.,
Volume 144, Number 2, January 25, 1999 255-266
Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
Zellweger syndrome and related diseases are
caused by defective import of peroxisomal matrix proteins. In all previously reported Zellweger syndrome
cell lines the defect could be assigned to the matrix protein import pathway since peroxisome membranes
were present, and import of integral peroxisomal membrane proteins was normal. However, we report here a
Zellweger syndrome patient (PBD061) with an unusual
cellular phenotype, an inability to import peroxisomal
membrane proteins. We also identified human PEX16, a novel integral peroxisomal membrane protein, and
found that PBD061 had inactivating mutations in the
PEX16 gene. Previous studies have suggested that peroxisomes arise from preexisting peroxisomes but we
find that expression of PEX16 restores the formation of
new peroxisomes in PBD061 cells. Peroxisome synthesis and peroxisomal membrane protein import could be
detected within 2-3 h of PEX16 injection and was followed by matrix protein import. These results demonstrate that peroxisomes do not necessarily arise from
division of preexisting peroxisomes. We propose that peroxisomes may form by either of two pathways: one
that involves PEX11-mediated division of preexisting
peroxisomes, and another that involves PEX16-mediated formation of peroxisomes in the absence of preexisting peroxisomes.
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