The peroxisome biogenesis disorders (PBDs) are a group of lethal autosomal-recessive diseases caused by defects in peroxisomal matrix protein import, with the concomitant loss of multiple peroxisomal enzyme activities. Ten complementation groups (CGs) have been identified for the PBDs, with CG1 accounting for 51% of all PBD patients. We identified the human orthologue of yeast PEX1, a gene required for peroxisomal matrix protein import. Expression of human PEX1 restored peroxisomal protein import in fibroblasts from 30 CG1 patients, and PEX1 mutations were detected in multiple CG1 probands. A common PEX1 allele, G843D, is present in approximately half of CG1 patients and has a deleterious effect on PEX1 activity. Phenotypic analysis of PEX1-deficient cells revealed severe defects in peroxisomal matrix protein import and destabilization of PEX5, the receptor for the type-1 peroxisomal targetting signal, even though peroxisomes were present in these cells and capable of importing peroxisomal membrane proteins. These data demonstrate an important role for PEX1 in peroxisome biogenesis and suggest that mutations in this gene are the most common cause of the PBDs.

Cell motility is a complex biological process, involved in development, inflammation, homeostasis, and pathological processes such as the invasion and metastatic spread of cancer. Here, we describe a genomic screen designed to identify inhibitors of cell migration. A library of 10,996 small interfering RNAs (targeting 5,234 human genes) was screened for their ability to block the migration of a highly motile ovarian carcinoma cell line, SKOV-3, by using a 384-well wound-healing assay coupled with automated microscopy and wound quantification. Two or more small interfering RNAs against four genes, CDK7, DYRK1B, MAP4K4 (

Peroxisomes are independent organelles found in virtually all eukaryotic cells. Genetic studies have identified more than 20 PEX genes that are required for peroxisome biogenesis. The role of most PEX gene products, peroxins, remains to be determined, but a variety of studies have established that Pex5p binds the type 1 peroxisomal targeting signal and is the import receptor for most newly synthesized peroxisomal matrix proteins. The steady-state abundance of Pex5p is unaffected in most pex mutants of the yeast Pichia pastoris but is severely reduced in pex4 and pex22 mutants and moderately reduced in pex1 and pex6 mutants. We used these subphenotypes to determine the epistatic relationships among several groups of pex mutants. Our results demonstrate that Pex4p acts after the peroxisome membrane synthesis factor Pex3p, the Pex5p docking factors Pex13p and Pex14p, the matrix protein import factors Pex8p, Pex10p, and Pex12p, and two other peroxins, Pex2p and Pex17p. Pex22p and the interacting AAA ATPases Pex1p and Pex6p were also found to act after Pex10p. Furthermore, Pex1p and Pex6p were found to act upstream of Pex4p and Pex22p. These results suggest that Pex1p, Pex4p, Pex6p, and Pex22p act late in peroxisomal matrix protein import, after matrix protein translocation. This hypothesis is supported by the phenotypes of the corresponding mutant strains. As has been shown previously for P. pastoris pex1, pex6, and pex22 mutant cells, we show here that pex4⌬ mutant cells contain peroxisomal membrane protein-containing peroxisomes that import residual amounts of peroxisomal matrix proteins.To form a functional peroxisome, peroxisome membranes must be generated and the subsequent import of both membrane and matrix proteins must occur. Various studies have established that both peroxisomal membrane proteins (PMPs) and peroxisomal matrix proteins are made in the cytosol and delivered posttranslationally to the peroxisome (26). However, the similarities between PMP import and peroxisomal matrix protein import appear to end there. Peroxisomal matrix proteins are targeted to the peroxisome lumen via the presence of either a PTS1 or a PTS2 targeting signal (40). The PTS1 signal, which consists of a -SKL sequence (or a conserved variant thereof) at the extreme carboxy terminus of the protein (16), is present on the vast majority of peroxisomal matrix proteins. The PTS2 signal consists of the sequence R/K-L/V/I-X 5 -H/Q-L/A near the amino terminus (41) and has so far been identified in only a handful of proteins. Both types of signals are recognized by specific receptors: Pex5p for the PTS1 signal (6, 29) and Pex7p for the PTS2 signal (27, 31). After binding to the receptor, matrix proteins are taken to the peroxisome surface and inserted into the organelle lumen through an as yet unknown mechanism. For Pex5p, it has been proposed that the receptor is then recycled back to the cytosol and can undergo further rounds of import (7). In contrast, PMPs lack PTS1 and PTS2 motifs (40), are imported independently of Pex5p and Pex7p ...