A cluster of arginine biosynthetic genes of Corynebacterium glutamicum ATCC 13032, comprising argJ, argB and argD as well as part of argC and argF, has been cloned by heterologous complementation of an Escherichia coli argE mutant. The gene order has been established as argCJBDF by sequencing the entire 4.4 kb cloned DNA fragment. The C. glutamicum argB gene can be transcribed in E. coli cells from an internal promoter located in the coding part of the preceding argJ gene, whereas transcription of the argJ gene appears vector-dependent. Expression of the corynebacterial argB gene is repressed by arginine in the native host but not in recombinant E. coli cells. Feedback inhibition of the corresponding N-acetylglutamate kinase activity was observed both in cell extracts of C. glutamicum and in recombinant E. coli argB auxotrophic strains. Extracts of E. coli cells carrying cloned corynebacterial DNA display an ornithine acetyltransferase activity (encoded by argJ) which alleviates the acetylornithinase (encoded by argE) deficiency of the enterobacterial host. In contrast to Bacillus stearothermophilus ornithine acetyltransferase which also exhibits acetylglutamate synthase activity, C. glutamicum ornithine acetyltransferase appears monofunctional. ArgA and ArgB proteins from different sources share highly significant similarities. The evolutionary implications of these data are discussed.

Matrix and ossification front changes were frequently observed and significantly associated with cartilage canals suggesting that they may be physiological changes associated with matrix remodelling and development. The collagen structure was variable through the growing epiphysis and a differential in biomechanical properties at focal sites may predispose them to injury.

The fact that after an hydrodynamic injection (35)S-DNA remains bound to the outside face of the plasma membrane for at least 1 h indicates that it is not, or very slowly, internalised during that period. The relatively small difference in the amount of DNA picked up by hepatocytes depending on the type of injection could not explain the absence of expression after a conventional injection and the strong expression after a hydrodynamic injection. If DNA enters the cells by endocytosis, even after an hydrodynamic injection, its persistence at the outside face of the plasma membrane could favour transfection by allowing hepatocytes to dispose for a relatively long time of a reservoir of intact DNA.

Most newly synthesized proteins destined for the lysosome reach this location via a specific intracellular pathway. In the Golgi, a phosphotransferase specifically labels lysosomal proteins with mannose 6-phosphate (Man-6-P). This modification is recognized by receptors that target the lysosomal proteins to the lysosome where, in most cell types, the Man-6-P recognition marker is rapidly removed. Despite extensive characterization of this pathway, the enzyme responsible for the removal of the targeting modification has remained elusive. In this study, we have identified this activity. Preliminary investigations using a cell-based bioassay were used to follow a dephosphorylation activity that was associated with the lysosomal fraction. This activity was high in the liver, where endogenous lysosomal proteins are efficiently dephosphorylated, but present at a much lower level in the brain, where the modification persists. This observation, combined with an analysis of the expression of lysosomal proteins in different tissues, led us to identify acid phosphatase 5 (ACP5) as a candidate for the enzyme that removes Man-6-P. Expression of ACP5 in N1E-115 neuroblastoma cells, which do not efficiently dephosphorylate lysosomal proteins, significantly decreased the steady state levels of Man6-P glycoproteins. Analysis of ACP5-deficient mice revealed that levels of Man-6-P glycoproteins were highly elevated in tissues that normally express ACP5, and this resulted from a failure to dephosphorylate lysosomal proteins. These results indicate a central role for ACP5 in removal of the Man-6-P recognition marker and open up new avenues to investigate the importance of this process in cell biology and medicine.dephosphorylation ͉ lysosome ͉ protein targeting T he lysosome is an acidic membrane-delimited organelle that plays a critical role in the cellular digestion of a diverse range of macromolecules including proteins, carbohydrates, nucleic acids, and lipids (1). These catabolic functions are conducted primarily by the concerted actions of over 60 soluble luminal hydrolases and accessory proteins, most of which are targeted to the lysosome by a common pathway (reviewed in ref. 2). Central to this pathway is a posttranslational modification that is largely specific to lysosomal proteins, mannose 6-phosphate (Man-6-P). Like other glycoproteins, soluble lysosomal proteins are synthesized in the endoplasmic reticulum and are cotranslationally glycosylated on select asparagine residues. As these proteins move through the secretory pathway, the lysosomal proteins are selectively recognized by a phosphotransferase that initiates a two-step reaction that results in the generation of the Man-6-P modification on specific N-linked oligosaccharides. The modified proteins are then recognized by two Man-6-P receptors (MPRs), the cation-dependent MPR and the cation-independent (CI-) MPR. These receptors bind the phosphorylated lysosomal proteins in the near neutral pH environment of the transGolgi network and travel to an acidic prelysosomal...

Our results show that the efficiency of hydrodynamics-based transfection depends on a process that takes place very quickly after injection and is not linked to a delay of DNA degradation and the persistence of a large proportion of DNA bound to hepatocytes of the plasma membrane, strongly suggesting that expression after a hydrodynamic injection is caused by a small proportion of DNA molecules that rapidly enter the cytosol probably by plasma membrane pores generated by the hydrodynamic pressure.

The protein array methodology is used to study DNA-protein and protein-protein interactions governing gene expression from the Bacillus stearothermophilus PargCo promoter-operator region. Using probes labelled with near-infrared fluorescence dyes with exitation characteristics close to 700 or 800 nm, it is possible to detect signals from proteins (purified or non-purified in Escherichia coli cell extracts) immobilised on a nitrocellulose membrane with a high sensitivity (almost 12 amol of a spotted protein for protein-DNA interactions). Protein array data are confirmed by other methods indicating that molecular interactions of the order 10(-7) M can be monitored with the proposed protein array approach. We show that the PargCo region is a target for binding at least three types of regulatory proteins, ArgR repressors from thermophilic bacteria, the E. coli RNA polymerase alpha subunit and cyclic AMP binding protein CRP. We also demonstrate that the high strength of the PargC promoter is related to an upstream element that binds to the E. coli RNA polymerase alpha subunit.

Peptide ligand-induced dimerization of the extracellular region of the epidermal growth factor receptor (sEGFR) is central to the signal transduction of many cellular processes. A small molecule microarray screen has been developed to search for non-peptide compounds able to bind to sEGFR. We describe the discovery of nitro-benzoxadiazole (NBD) compounds that enhance tyrosine phosphorylation of EGFR and thereby trigger downstream signaling pathways and other receptor tyrosine kinases in cancer cells. The protein phosphorylation profile in cells exposed to NBD compounds is to some extent reminiscent of the profile induced by the cognate ligand. Experimental studies indicate that the small compounds bind to the dimerization domain of sEGFR, and generate stable dimers providing allosteric activation of the receptor. Moreover, receptor phosphorylation is associated with inhibition of PTP-1B phosphatase. Our data offer a promising paradigm for investigating new aspects of signal transduction mediated by EGFR in cancer cells exposed to electrophilic NBD compounds.

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