Cross-coupling of signal transduction pathways: zinc finger meets leucine zipper.

Cell proliferation and cellular differentiation are often thought of as opposing phenomena. The molecular mechanisms by which steroid, retinoid and thyroid hormones inhibit cellular proliferation and by which growth factors stimulate this process are poorly understood. We discuss recent evidence suggesting that these two signal transduction pathways converge through a process referred to as 'cross-coupling', which involves a possible interaction between steroid hormone receptors and the c-Jun oncoprotein.     

The torpedo (DER) receptor tyrosine kinase is required at multiple times during Drosophila embryogenesis.

The torpedo (DER) gene of Drosophila, which encodes a receptor tyrosine kinase of the EGF receptor subfamily, is essential for oogenesis, embryogenesis and imaginal disc development. To gain insight into the nature of the signals transduced by the torpedo product, we have characterized the gene's loss-of-function phenotype in the embryo. Through the induction of germline clones, we provide a genetic demonstration that maternal torpedo product does not contribute to zygotic development. Thus, the embryonic lethal phenotypes examined accurately reflect the consequences of eliminating all gene activity from the zygote. Temperature-shift experiments with the conditional allele topIF26 show that torpedo is required at two distinct times during embryonic development: the gene is first needed for germband retraction and for the production of anterior, posterior and ventral cuticle, then later for the secretion of ventral denticles. Since denticle formation can be severely disrupted in topIF26 animals without affecting cuticle production, the early and late requirements for torpedo appear to be functionally unrelated. torpedo, therefore, is required at multiple times in the development of the ventral epidermis, and may transduce qualitatively different signals. Since the early requirement for torpedo correlates with the first visible defect in embryonic development, increased cell death in the amnioserosa, cephalic ectoderm and ventral epidermis, the abnormalities in cuticle production and germband shortening seen in the mutant may be secondary consequences of a primary defect in cell viability. Given that the onset of cell death in torpedo embryos is not preceded by any obvious defects in mitogenesis, the establishment of cell identities or the maintenance of gene expression, it is possible that torpedo transduces a signal necessary for cell survival per se during early embryogenesis. During late embryogenesis, torpedo may mediate the reception of a second signal which regulates ventral epidermal cell differentiation.     

Monitoring and control of biotechnological production processes by Bio-FET-FIA-sensors

Summary Single and multisensor field effect transistors (FET) with a pH-sensitive Si/SiO₂/Si₃N₄/Ta₂O₅-gate and reference electrode (for single sensor) were developed and used for manufacturing the following biological (Bio)-FETs: for glucose analysis, glucose oxidase-FET (GOD-FET); for urea analysis, urease-FET; and for cephalosporin C analysis, cephalosporinase-FET. The GOD-FETs were integrated into flow injection analysis (FIA) of the Eppendorf variables analyser (EVA) system and used for monitoring the glucose concentration in microbial cultivation and production processes with recombinant Escherichia coli K12 MF, recombinant E. coli JM103, Saccharomyces cerevisiae H620, and Candida boidinii. Urease-FET-FIA was used to monitor the urea concentration in a simulated cultivation of Cephalosporium acremonium and urease-FET-FIA and GOD-FET-FIA for the monitoring of urea and glucose concentrations in simulated S. cerevisiae cultivations.     

Gramicidin in chromatophores of Rhodobacter sphaeroides

Chromatophores of Rhodobacter sphaeroides were excited with light flashes to generate a transmembrane electrical potential difference. The electric relaxation was measured by electrochromic absorption changes as a function of added gramicidin. At low gramicidin/bacteriochlorophyll (BChl) molar ratios the decay of the electrochromic absorption changes showed a biphasic behaviour, with a fast phase relaxing at some s, and a slow phase relaxing at more than 100 ms. This was attributable to a mixture of vesicles containing gramicidin dimers with others containing none. The concentration dependence of this effect was linear. This implied full dimerization of gramicidin. The data were interpreted to yield an average bacteriochlorophyll content per chromatophore of 770(±150) and the conductance of a single gramicidin dimer in the chromatophore membrane of 15(±4) pS (in about 115 mM KCl).Abbreviations BChl Bacteriochlorphyll - tricine N-Tris[hydroxymethyllmethylglycine Offprint requests to: W. Junge     

Formation of acetic acid from cellulosic substrates byFusarium oxysporum

Summary Four strains of Fusarium oxysporum and a strain of Monilia brunnae were screened for their ability to convert cellulosic substrates into ethanol/acetic acid. These strains were found to utilize cellulose and produce extracellular cellulases. However, only F. oxysporum 841 was found to convert glucose, xylose, and cellulose into ethanol and acetic acid as major end-products under microaerobic conditions. Acetic acid at a level of 4.7 g/l resulted in a single-step process on potato pulp medium, indicating the potential of the strain for converting cellulosic substrates into acetic acid. Offprint requests to: K. Schügerl     

N-terminal amino-acid sequence of pig kidney dipeptidyl peptidase IV solubilized by autolysis.

The N-terminal amino-acid sequence of the intrinsic membrane protein dipeptidyl peptidase IV (DP IV) was determined. The protein was isolated from pig kidney and solubilized by autolysis at pH 3.8. The first 34 amino acids were sequenced and indicated approximately 78% identity to the N-terminal sequence of rat liver DP IV.     

Bacteriophage receptors of Lactococcus lactis subsp. 'diacetylactis' F7/2 and Lactococcus lactis subsp. cremoris Wg2-1

Bacteriophage P008 revealed irreversible and uniform adsorption to cell walls of L. lactis subsp. 'diacetylactis' F7/2, whereas phage P127 adsorbed reversibly to a limited number of receptor sites on cell walls of L. lactis subsp. cremoris Wg2-1. Neither extraction of lipids, cell wall- and membrane-teichoic acids nor enzymatic degradation of proteins altered the binding efficiencies of both cell wall fractions. However, phage binding was inhibited, when cell walls were subjected to lysozyme, metaperiodate, or acid treatments. This reflects that a carbohydrate component embedded in the peptidoglycan matrix is part of the phage receptors of strains F7/2 and Wg2-1.     

Isolation and characterization of two proteoheparan sulfate species of calf arterial tissue

When calf aortic tissue, preincubated under organ culture conditions in the presence of [35S]sulfate, was submitted to a sequential collagenase and elastase digestion and guanidinium chloride extraction, the bulk of proteoheparan sulfate was obtained in the elastase fraction. Ion-exchange chromatography on DEAE-cellulose of the elastase digest under dissociative conditions yielded a proteoglycan fraction that contained heparan sulfate as the sole glycosaminoglycan. The proteoheparan sulfate fraction was resolved into a high-molecular-mass (P-HS 1) and a low-molecular-mass (P-HS 2) fraction by gel filtration on Sephacryl S-400. P-HS 1 has a Mr of 175,000 and possesses four heparan sulfate side-chains (Mr 32,000) covalently bound to the protein core via a galactose- and xylose-containing polysaccharide-protein binding region. The protein core (Mr 38,000), which was obtained after deglycosylation of PG-HS 1 with trifluormethane sulfonic acid, contained in addition a few N-glycosidically linked oligosaccharide units representing a complex type with terminal neuraminic acid residues. P-HS 2 is a single-chain peptidoheparan sulfate of Mr of 38,000 containing one heparan sulfate chain (Mr 32,000) linked to a polypeptide (Mr 6000). The ratio of specific radioactivities of P-HS 1 and P-HS 2 was 1:0.66.     

The interaction of ethanol and exogenous arachidonic acid in the generation of extracellular messengers by mouse peritoneal macrophages

It is increasingly recognized that macrophages play a crucial role in the development of chronic inflammatory states such as alcoholic liver disease. These cells can metabolize free arachidonic acid in the absence of a discernible trigger. The present study was undertaken to examine the short-term effects of ethanol on the generation of these exogenous arachidonate-derived extracellular mediators. Ethanol caused a dose-dependent decrease in the production of both cyclooxygenase and lipoxygenase metabolites. Similar effects were observed on the esterification of exogenous arachidonate into cellular lipids. To characterize further the effects of ethanol on exogenous arachidonic acid metabolism, we studied the short-term responses displayed by macrophages challenged with another soluble stimulus; the tumor-promoting agent phorbol myristate acetate. We observed an inhibition by ethanol of the superoxide anion response triggered by phorbol myristate acetate similar to that observed for exogenous arachidonate oxygenation. Our results show that ethanol can inhibit these soluble stimuli-elicited responses, possibly through its disorganizing effect on plasma membrane.