A new method for predicting signal sequence cleavage sites.

A new method for identifying secretory signal sequences and for predicting the site of cleavage between a signal sequence and the mature exported protein is described. The predictive accuracy is estimated to be around 75-80% for both prokaryotic and eukaryotic proteins.     

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.     

Interspecific crosses inHordeum (Poaceae)

A crossing programme including 30 species and 40 cytotypes within the genusHordeum was undertaken. Viable hybrids were obtained in 302 combinations, 15 of which were intraspecific. Differences in seed set and in germination were observed in crosses between different groups of species. Obtaining crosses between different taxonomic groups was generally more difficult when diploid material was used. Some species, e.g.,H. lechleri, H. jubatum, andH. brachyantherum showed a higher crossability than others. The chromosome numbers of the hybrids were usually those expected from the parental numbers but aneuploid series around the expected numbers were rather frequent. Three cases of unreduced gametes were found. Selective chromosome elimination was restricted to combinations including eitherH. vulgare orH. bulbosum.—Despite a very diverse morphology, all South American diploid species together with the two North American diploidsH. intercedens andH. pusillum appear to be closely related. The hexaploid American speciesH. procerum, H. lechleri, andH. arizonicum are also related. The two North American tetraploid speciesH. jubatum andH. brachyantherum sometimes form semifertile hybrids. The Asiatic speciesH. roshevitzii appears to be related to both North and South American taxa.     

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.     

Isolation and characterization of a collagen-binding glycoprotein from chondrocyte membranes

A collagen-binding glycoprotein was isolated from purified chick chondrocyte surface membranes by affinity chromatography on type II collagen-Sepharose. The purified glycoprotein has an apparent mol. wt. of 31,000 and binds to native chick collagen types I, II, III, V and M. Although it contains 30% carbohydrates, the majority of which is fucose, it is hydrophobic and soluble only in detergents. The integral membrane protein character of the 31-K protein became apparent from its ability to insert into lecithin vesicles. Liposome-inserted 31-K protein binds 125I-labelled type II collagen in the presence of 0.5 M NaCl, while detergent-solubilized 31-K protein is dissociated from type II collagen by 0.05-0.1 M NaCl. Electron microscopic studies employing the rotary shadowing technique indicate that 31-K protein particles bind to the ends of collagen molecules. We propose that this glycoprotein serves as anchorage site for extracellular collagen to the chondrocyte membrane and thus may be involved in cell-matrix interactions in cartilage.     

Lymphoid cell subclasses in rejecting renal allograft in the rat

We have quantitated the frequency of lymphoid cell subsets in rejecting renal allografts and in the spleen of the allograft recipient during drug-unmodified rejection in the rat. The number of inflammatory (white) cells in the graft was approximately similar to the number of white cells responding to the allograft in the recipient spleen. The inflammatory population of the graft consisted of lymphoid cells and mononuclear phagocytes, with increasing numbers of macrophages toward the end of rejection. Analysis of allograft cellular dispersates with monoclonal antibodies directed to the lymphoid cell subsets demonstrated that although the majority of allograft-infiltrating lymphocytes were T cells, a sizable B-cell proliferation and immunoglobulin synthesis was associated with the inflammatory response of rejection. Within the T-cell subset, the T suppressor/killer cells predominated in the graft whereas the predominant lymphoid cell subset responding to the allograft in the recipient spleen was the T helper cell.