How signal sequences maintain cleavage specificity

The specificity of the signal sequence cleavage reaction has been postulated to reside in a signal peptidase active site that can bind only to particular (i, i + 2) pairs of amino acids. In this paper, we present further patterns of non-random amino acid utilization in a region around in vivo cleavage sites, and show that they can be interpreted in terms of selection acting to reduce the number of potential competing sites in the vicinity of the correct one.     

Temperature-sensitive mutants of MH2 avian leukemia virus that map in the v-mil and the v-myc oncogene respectively.

MH2 is an avian retrovirus that contains the v-mil and v-myc oncogenes. In vitro it transforms chick macrophages that are capable of proliferation in the absence of growth factor. Earlier work showed that v-myc induces macrophage transformation and that v-mil induces the production of chicken myelomonocytic growth factor (cMGF), thus generating an autocrine system. We describe the isolation of temperature-sensitive (ts) mutants of MH2 virus. As suggested by marker rescue experiments, one mutant bears a ts lesion in v-mil, whereas the other carries a mutation in v-myc. Ts v-mil MH2-transformed macrophages become factor-dependent at the non-permissive temperature (42 degrees C), while ts-v-myc MH2-transformed macrophages cease growing and acquire a more normal macrophage phenotype at 42 degrees C irrespective of the presence of cMGF. Both phenotypes can be reversed by backshift to the permissive temperature. These results suggest that the gene products of v-mil and v-myc function independently of each other and that v-mil is necessary for the maintenance of autocrine growth, whereas v-myc is required to maintain the transformed phenotype.     

Tracing of single fibers of the nervus terminalis in the goldfish brain

Summary Central projections of the nervus terminalis (n.t.) in the goldfish were investigated using cobalt- and horseradish peroxidase-tracing techniques. Single n.t. fibers were identified after unilateral application of cobalt chloride-lysine to the rostral olfactory bulb. The central course and branching patterns of individual n.t. fibers were studied in serial sections. Eight types of n.t. fibers are differentiated according to pathways and projection patterns. Projection areas of the n.t. include the contralateral olfactory bulb, the ipsilateral periventricular preoptic nucleus, both retinae, the caudal zone of the periventricular hypothalamus bilaterally, and the rostral optic tectum bilaterally. N.t. fibers cross to contralateral targets in the anterior commissure, the optic chiasma, the horizontal commissure, the posterior commissure, and possibly the habenular commissure. We propose criteria that differentiate central n.t. fibers from those of the classical secondary olfactory projections. Branching patterns of eight n.t. fiber types are described. Mesencephalic projections of the n.t. and of secondary olfactory fibers are compared and discussed with regard to prior reports on the olfactory system of teleosts. Further fiber types for which the association with the n.t. could not be established with certainty were traced to the torus longitudinalis, the torus semicircularis, and to the superior reticular nucleus on the ipsilateral side.     

A neural cocktail-party processor

Sensory segmentation is an outstanding unsolved problem of theoretical, practical and technical importance. The basic idea of a solution is described in the form of a model. The response of neurons within the sensory field is temporally unstable. Segmentation is expressed by synchronization within segments and desynchronization between segments. Correlations are generated by an autonomous pattern formation process. Neuronal coupling is the result both of peripheral evidence (similarity of local quality) and of central evidence (common membership in a stored pattern). The model is consistent with known anatomy and physiology. However, a new physiological function, synaptic modulation, has to be postulated. The present paper restricts explicit treatment to the peripheral evidence represented by amplitude modulations globally present in all components of a sound spectrum. Generalization to arbitrary sensory qualities will be the subject of a later paper. The model is an application and illustration of the Correlation Theory of brain function.This work has been supported by Grant I/37-821 of the Stiftung Volkswagenwerk.     

Biosynthesis and maturation of arylsulfatase B in normal and mutant cultured human fibroblasts

The biosynthesis of arylsulfatase B in normal and mutant human skin fibroblasts was studied by metabolic labeling with radioactive amino acids, monosaccharides, or 32Pi and by specific immunoprecipitation followed by polyacrylamide gel electrophoresis and fluorography. Three major polypeptides with apparent molecular weights of 47,000, 40,000, and 31,000 were found intracellularly and one of 64,000 in the medium. Pulse-chase labeling and uptake experiments showed that arylsulfatase B synthesized and secreted as a 64,000 precursor was intracellularly processed within less than 24 h via short lived intermediates to two different forms. Form I (chains of 47,000 and 11,500) was labeled earlier and was about twice as stable as form II (chains of 40,000 and 31,000). The secreted 64,000 precursor and the 40,000 chain of form II contained oligosaccharides resistant to endo-beta-N-acetylglucosaminidase H. In the other chains mainly cleavable and phosphorylated oligosaccharides were found. Arylsulfatase B activity was associated with the 64,000 precursor and with form I, but not with form II. Fibroblasts of four patients with the severe form of mucopolysaccharidosis type VI, which were deficient in arylsulfatase B activity, synthesized and secreted the 64,000 precursor at a normal rate. This precursor, however, had little if any catalytic activity and one of its mature forms (I) was rapidly degraded.     

Chronic caffeine consumption potentiates the hypotensive action of circulating adenosine

Mean arterial blood pressure was correlated with arterial plasma adenosine levels during intravenous adenosine infusion in unanesthetized, unrestrained rats. Elevation of plasma adenosine to 5 to 6 microM (normal range 1.6 to 4.6 microM) depressed mean arterial pressure by 20 to 30 percent: this was blocked by a single caffeine injection (15 mg/kg). In contrast, caffeine consumption for 3 weeks, followed by a 1-day washout, markedly potentiated responses to adenosine, plasma levels in the 2 to 4 microM range causing 30 to 40 percent reductions in mean arterial pressure. These observations suggest that chronic occupancy of cardiovascular adenosine receptors by caffeine can enhance tissue responsiveness to adenosine, and that endogenous adenosine might act as a circulating hormone.     

Identification and characterization of gp TFA-1, a guinea pig T cell surface antigen associated with T cell function

Monoclonal antibodies (Ab) were produced that specifically recognized guinea pig T cells. FACS analysis revealed that Ab 188 bound to the majority of peripheral T lymphocytes of strain 2 and strain 13 guinea pigs and to a minor population of thymocytes. It failed to react with the Ia-bearing guinea pig B cell leukemia line EN-L2C, with macrophages, bone marrow cells, erythrocytes, or thrombocytes. Treatment of T cells with Ab 188 and complement prevented T cell activation. Culturing primed T cells with antigen- or mitogen-pulsed syngeneic or with allogeneic macrophages in the continuous presence of Ab 188 produced a marked, dose-dependent inhibition of T cell proliferation. The antigen defined by Ab 188 was therefore designated guinea pig T lymphocyte function-associated antigen-1, gp TFA-1. The magnitude of inhibition by Ab 188 varied between 65 and 85% whereas three other antibodies to guinea pig T cells had no inhibitory effect on T cell proliferation. Time course experiments revealed that gp TFA-1 is critically involved in an early phase of T cell activation. Maximal inhibition was achieved only if the antibody was present from the beginning of the cell culture; the addition of antibody after 24 hr of culture no longer had an inhibitory effect. Ab 188 did not induce T cell mitogenesis. Two-dimensional analysis (one-dimensional, IEF; two-dimensional, SDS-PAGE) of immunoprecipitates obtained from NP40 lysates of [35S]methionine-labeled T cell blasts indicated that a molecule was specifically precipitated that consisted of two noncovalently associated polypeptide chains with apparent m.w. of 43,000 and 38,000. Both subunits displayed extensive charge heterogeneity focusing at an average isoelectric point of 5.0 and 6.5, respectively. The gp TFA-1 molecule exhibits striking similarities in its functional and structural properties to recently described clonotypically expressed T cell glycoproteins, which were shown to be involved in antigen recognition by T cells in the murine and human systems.     

Stoffwechsel-Regulation aerober Zellsuspensionen vonSaccharomyces carlsbergensis nach Glucosezugabe

Zusammenfassung Wird eine ausgehungerte aerobe Zellsuspension vonSaccharomyces carlsbergensis mit Glucose gefüttert, dann ist eine deutliche Stimulierung des O₂-Verbrauchs zu registrieren. Mit Hilfe verschiedener Meßmethoden wurde der Verlauf dieser nicht-linearen O₂-Abnahme analysiert und mit den gleichzeitig auftretenden Konzentrationsänderungen einiger glykolytischer Metabolite korreliert.Dabei zeigt sich, daß ca. 20–60 Sekunden nach Glucosezugabe die Rate des O₂-Verbrauchs abnimmt und gleichzeitig eine deutliche Äthanol-Synthese einsetzt, obgleich der O₂-Partialdruck zu diesem Zeitpunkt noch etwa halbmaximal ist.

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Metabolite-regulation of aerobic cell-suspension ofSaccharomyces carlsbergensis after feeding with glucose. I. Shift from respiration to aerobic fermentation

Summary After feeding with glucose, an aerobic starved cell-suspension ofSaccharomyces carlsbergensis shows an increasing of oxygen consumption. This stimulation is not linear during the transition from high to low oxygen-level.For this aerobic phase the regulated fluxes of some metabolites are analyzed. It could be shown that with highest oxygen consumption an ethanol synthesis is starting.

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Herrn Prof. Dr.A. Betz danke ich an dieser Stelle für viele wertvolle Hinweise zur Interpretation der hier beschriebenen Ergebnisse. Die gewissenhafte technische Assistenz erfolgte durch FrauR. Hinrichs. Die Durchführung dieser Arbeit wurde durch Sachbeihilfen der Stiftung Volkswagenwerk und der Deutschen Forschungsgemeinschaft ermöglicht.     

Behavioral responses to linear accelerations in blind goldfish

Blind goldfish were subjected to linear accelerations on a motor car and on a parallel swing. Moyements of the fish in a tank during the accelerations were recorded with a movie camera. During the horizontal acceleration, the fish aligns his longitudinal axis in a plane perpendicular to the direction of an apparent gravity with the fish's back pointing away from the direction of this apparent gravity vector. This is similar to the manner in which the fish usually aligns himself horizontally in response to the vertically downward terrestrial gravity and can therefore be termed gravity reference response. It is concluded that blind goldfish cannot distinguish between otolith displacements caused by passive tilts and equivalent otolith displacements caused by moderate inertial forces during rectilinear acceleration. With a horizontal jerk of higher magnitude, two additional responses can occur: horizontal 180° turns following tailward jerks and straight forward darting following noseward jerks.This work was supported by NASA Grant No. NGR 23-005-201.