Secondary structure features of ribosomal RNA species within intact ribosomal subunits and efficiency of RNA-protein interactions in thermoacidophilic (Caldariella acidophila, Bacillus acidocaldarius) and mesophilic (Escherichia coli) bacteria

Ribosomal subunits of Caldariella acidophila (max.growth temp., 90 degrees C) have been compared to subunits of Bacillus acidocaldarius (max. growth temp., 70 degrees C) and Escherichia coli (max. growth temp., 47 degrees C) with respect to (a) bihelical content of rRNA; (b) G . C content of bihelical domains and (c) tightness of rRNA-protein interactions. The principal results are as follows. Subunits of C. acidophilia ribosomes (Tm = 90-93 degrees C) exhibit considerable thermal tolerance over their B. acidocaldarius (Tm = 77 degrees C) and E. coli counterparts (Tm = 72 degrees C). Based on the "melting' hyperchromicities of the intact ribosomal subunits a 51-55% fraction of the nucleotides appears to participate in hydrogen-bonded base pairing regardless of ribosome source, whereas a larger fraction, 67-70%, appears to be involved in hydrogen bonding in the naked rRNA species. The G . C content of bihelical domains of both free and ribosome-bound rRNA increases with increasing thermophily; based on hyperchromicity dispersion spectra of intact subunits and free rRNA, the bihelical parts of C. acidophila rRNA are estimated to contain 63-64% G . C, compared to 58.5% G . C for B. acidocaldarius and 55% G . C for E. coli. The increment of ribosome Tm values with increasing thermophily is greater than the increase in Tm for the free rRNA, indicating that within ribosomes bihelical domains of the thermophile rRNA species are stabilized more efficiently than their mesophile counterparts by proteins or/ and other component(s). The efficiency of the rRNA-protein interactions in the mesophile and thermophile ribosomes has been probed by comparing the releases, with LiCl-urea, of the rRNA species from the corresponding ribosomal subunits stuck to a Celite column through their protein moiety; it has been established that the release of C. acidophila rRNA from the Celite-bound ribosomes occurs at salt-urea concentrations about 4-fold higher than those required to release rRNA from Celite-bound E. coli ribosomes. Compared to E. coli the C. acidophila 50 and 30 S ribosomal subunits are considerably less susceptible to treatment designed to promote ribosome unfolding through depletion of magnesium ions.     

Monolayer black membranes from bipolar lipids of archaebacteria and their temperature-induced structural changes

The membrane of Caldariella acidophila, an extreme thermophilic archaebacterium, is characterized by unusual bipolar complex lipids. They consist of two nonequivalent polar heads, linked by a C40 alkylic component. The molecular organization of these lipids in the plasma membrane is still a matter of study. In this paper, we present current-voltage measurements on artificial bipolar lipid membranes, indicating that molecules are indeed organized as a covalently bound bilayer, in which each molecule is completely stretched and spans its entire thickness. Furthermore, conformational transitions of these artificial membranes (which could be formed only above 70 degrees C from a lipid/squalene dispersion) are analyzed in the 80 to 15 degrees C temperature range. Abrupt variations in capacitance and valinomycin-induced conductance seem to indicate the occurrence of at least two structural changes. Measurements are also extended to different solvent systems. Results are consistent with the picture of a monolayer bipolar lipid membrane in which few solvent molecules align themselves parallel to the lipophilic chains. The amount of solvent as well as the temperature at which conformational transitions occur, depend on the solvent system in which the lipid is dispersed.     

Differential regulation of HLA-DR mRNAs and cell surface antigens by interferon

Human interferons-alpha, -beta and -gamma enhance HLA-DR mRNAs in all the human lymphoblastoid and melanoma cell lines studied. The increase concerns both alpha and beta chain mRNAs. Moreover, we show that immune interferon-gamma preferentially enhances class II MHC mRNA. This effect of IFN-gamma on the synthesis of alpha and beta HLA-DR chains has been also analysed by immunoprecipitation. It is abolished by a monoclonal antibody directed against human IFN-gamma. The effect of interferon on the cell surface level of HLA-DR molecules does not always correspond to the enhancement of HLA-DR mRNA. Our experiments suggest that this discrepancy between the enhancement of HLA-DR mRNA and cell surface antigen might be due to a constitutively high level of the corresponding antigens on several of the human cells studied.     

Diphosphoglycerate mutase and 2,3-diphosphoglycerate phosphatase activities of red cells: comparative electrophoretic study

Erythrocyte diphosphoglycerate mutase (EC 2.7.5.4.) and 2,3-diphosphoglycerate phosphatase (EC 3.1.3.13.) activities of normal human adults, and DPG mutase deficient subject as well as of several animal species were subjected to electrophoretic study on starch gel. In U.V. light 2,3-diphosphoglycerate phosphatase activity was revealed as a band of fluorescence decrease on a fluorescent background, by the oxydation of NADH, whereas diphosphoglycerate mutase appeared as a fluorescent zone. It was found that the electrophoretic pattern of both DPG mutase and 2,3-DPG phosphatase activities was different from one species to the other, but that, in each species, 2,3-DPG phosphatase activity showed the same electrophoretic pattern as DPG mutase activity.     

The primary structure of human secretogranin II, a widespread tyrosine-sulfated secretory granule protein that exhibits low pH- and calcium-induced aggregation

Secretogranin II (previously also called chromogranin C) is a tyrosine-sulfated secretory protein found in secretory granules in a wide variety of endocrine cells and neurons. Here, we have determined the primary structure of human secretogranin II from a full length cDNA clone and have investigated its properties, predicted from the sequence, by studying the behavior of purified secretogranin II under conditions characteristic of the milieu of secretory granules. Analysis of a 2.35-kilobase cDNA clone isolated from a human pituitary library and identified as secretogranin II by various criteria showed that human presecretogranin II is a 617-residue polypeptide containing an NH2-terminal located signal peptide. Secretogranin II lacks the disulfide-bonded loop structure near the NH2 terminus which is conserved in chromogranin A and chromogranin B (secretogranin I), two other widespread constituents of neuroendocrine secretory granules, but like the latter two proteins contains (i) an -E-N/S-L-X-A/D-X-D/E-X-E-L- motif and (ii) multiple potential dibasic cleavage sites for the generation of smaller, perhaps biologically active peptides. Another structural feature that secretogranin II shares with chromogranin A and chromogranin B (secretogranin I) is the abundance of acidic residues all along the polypeptide chain whose negative charge must somehow be neutralized to allow condensation and packaging of the protein into secretory granules. Experiments with purified secretogranin II showed that in the presence of 10 mM calcium at pH 5.2, conditions characteristic of the milieu of neuroendocrine secretory granules, this protein formed aggregates. Immunoglobulin G, a secretory protein that in vivo is not packaged into secretory granules, did not form aggregates under these in vitro conditions and was excluded from the secretogranin II aggregates. Very little aggregation of secretogranin II was observed in the absence of calcium at pH 5.2 or in the presence of calcium at neutral pH. In vivo, ammonium chloride, which is known to neutralize the pH of acidic intracellular compartments, inhibited the packaging of newly synthesized secretogranin II into secretory granules. Our results suggest that the low pH- and calcium-induced aggregation of secretogranin II may be important for the organization of the secretory granule matrix and raise the possibility that aggregation of secretogranin II may be involved in its sorting to secretory granules.     

Arg74 in HLA-DRBI and DRB3 controls a DR3-related epitope

TR81 is a specificity closely related to or identical with DR3. In Caucasoids two amino acids, Tyr at position 26 and Arg at position 74 of HLA class II DR chains, have been found to be associated with the presence of TR81. Recently, a variant of DRBI *03 identified in American Blacks has been shown to possess Arg at position 74 but Phe at position 26. This codon combination is found to be present in four other cell lines where it still specifies the TR81 determinant. This suggests that the TR81 specificity is uniquely dependent on the presence of Arg at position 74.     

Fruit infesting tephritids [Dipt.: Tephritidae] and associated parasitoids in Chiapas,Mexico

A total of 1,302 parasitoids representing 8 species and 4 families were recovered from 9,818 fruit fly host fruits sampled. The most common parasitoid species wasDiachasmimorpha longicaudata (Ashmead). Average percent parasitism ranged between 0.44 and 29.23%. Parasitoid emergence data indicate thatAnastrepha ludens (Loew),A. obliqua (Sein),A. serpentina (Wiedeman),A. striata (Schiner) andToxotrypana curvicauda (Gerstaecker) were subject to parasitism. We provide information on the population fluctuation ofAnastrepha ludens, A. obliqua, A. serpentina, A. distincta (Greene),A. striata, A. fraterculus (Wiedeman),A. chiclayae (Greene),A. montei (Costa Lima),A. leptozona (Hendel) andA. tripunctata (Wulp).Anastrepha ludens andA. obliqua were the most common species, representing 95.3% of all fruit fly species caught in McPhail traps.