Heat and sodium arsenite act synergistically on the induction of heat shock gene expression in Xenopus laevis A6 cells

Heat shock protein (HSP) synthesis was studied in the Xenopus epithelial cell line A6 in response to heat and sodium arsenite, either singly or together. Temperatures of 33-35 degrees C consistently brought about the synthesis of HSPs at 87, 73, 70, 54, 31, and 30 kilodaltons (kDa), whereas sodium arsenite at 25-100 microM induced the synthesis of HSPs at 73 and 70 kDa. In cultures exposed to 10 microM sodium arsenite at 30 degrees C, HSP synthesis in the 68- to 73-kDa and 29- to 31-kDa regions was much greater than the HSP synthesis in response to each treatment individually. RNA dot blot analysis using homologous genomic subclones revealed that heat shock induced the accumulation of HSP 70 and 30 mRNAs. The sizes of the HSP 70 and 30 mRNAs determined by Northern hybridization were 2.7 and 1.5 kilobases, respectively. Sodium arsenite (10-100 microM) also induced the accumulation of both HSP 70 and 30 mRNAs. Finally, a mild heat shock (30 degrees C) plus a low concentration of sodium arsenite (10 microM) acted synergistically on HSP 70 and 30 mRNA accumulation in A6 cells. Thus sodium arsenite and heat act synergistically at the level of both HSP synthesis and HSP mRNA accumulation.     

Activation of the alternative complement pathway by Leishmania promastigotes: parasite lysis and attachment to macrophages

When exposed to normal human or guinea pig sera, promastigotes of Leishmania enriettii and L. tropica activate the complement cascade by the alternative pathway and fix C3 on their surfaces. In high (25%) serum concentrations, the result of complement activation is parasite lysis. At lower concentrations (4%), complement fixation results in enhanced parasite binding and uptake into murine peritoneal macrophages. Parasites are lysed in normal guinea pig, C4-deficient guinea pig, normal human, and C2-deficient human sera when they are incubated at 37 degrees C for 30 min. Fetal calf and normal mouse sera are poorly lytic. Lysis requires Mg++ but not Ca++, is mediated by heat labile (56 degrees C, 30 min) component(s), and does not occur when the incubations are maintained at 4 degrees C. Guinea pig serum preadsorbed with promastigotes of L. tropica in EDTA at 4 degrees C for 30 min is fully lytic. Immunofluorescence studies with anti-C3 antibodies show that under these conditions C3 is deposited on the surface of the parasite. The serum-dependent binding of parasites to macrophages is also mediated by heat-labile, nonadsorbable factor(s) present in normal guinea pig and mouse sera, as well as C2-deficient and C4-deficient sera. The serum-dependent macrophage recognition mechanism is trypsin sensitive but relatively resistant to chymotrypsin. Parasites but not macrophages can be presensitized at room temperature with low levels (8%) of serum to enhance their binding to macrophages. Presensitization does not occur at 4 degrees C. These results show that Leishmania promastigotes of several species can fix complement by activating the alternative complement pathway. This may then result either in parasite lysis or in an accelerated uptake of the parasite into phagocytic cells. In vivo, the biologic outcome of infection may reflect a balance between extracellular lysis and enhanced uptake into phagocytic cells.     

The transfer of 5'-methylthioadenosine from B82 cells through the medium to CHW-1102 cells

The Chinese hamster cell line. CHW-1102, which is deficient in hypoxanthine guanine phosphoribosyl transferase (HGPRT+), incorporated a [3H]purine metabolite(s) from medium in which B82 cells, but not V79, A9 and BHK cells, had been grown for 24 h with [3H]hypoxanthine. A thin-layer chromatographic comparison of the medium revealed a large radioactive peak that was unique to the B82 medium and co-chromatographed with methylthioadenosine (MTA), but not with most other common purine bases and nucleosides. The addition of either MTA, adenine, or adenosine to B82 medium reduced the amount of radioactive material incorporated by CHW-1102 cells. Methylglyoxal bis(guanylhydrazone) inhibited the production of the [3H]metabolite(s) that were incorporated from B82 medium by CHW-1102 cells. Little MTA phosphorylase activity was detected in the mouse L cell lines, L929, B82, and A9, but activity was present in CHW-1102 cells. These results suggest that one of the metabolites in B82 medium is [3H]MTA, and this is taken up and cleaved by CHW-1102 cells to yield [3H]adenine, which is incorporated into nucleic acids. This accounts for the majority of contact-independent metabolite transfer (CIMT). In cocultures some interactions between B82 and CHW-1102 cells were positive for contact-dependent metabolite transfer (CDMT) or metabolic cooperation.     

Growth Rates of Sulfolobus acidocaldarius in Nature

Turnover times for water passing through several Sulfolobus acidocaldarius-containing springs were determined by measuring the dilution rates of small amounts of sodium chloride that were added to the springs. Chloride was diluted out exponentially, while concentrations of the bacteria remained constant. Additionally, temperature, pH, and chemical composition of the springs also remained constant during the time that the chloride was being diluted. The springs are thus steady-state systems, and since the rates of bacterial growth must be at least equal to the chloride dilution rates, minimal doubling times for the bacterial populations can be calculated. Half-times for chloride dilution, equivalent to bacterial doubling times, were on the order of 10 to 20 h for springs ranging in volume from about 20 to 2,000 liters, but approximately 30 days for two larger springs of about 1 million liters. Formaldehyde-fixed cells of a serologically distinguishable strain of S. acidocaldarius were also added as markers to four of the smaller springs, and the dilution rates of these bacteria were compared with the chloride dilution rates. The rates agreed reasonably well, thus verifying the growth rates obtained from the chloride dilution rates. In three springs, exponential growth was studied by draining the springs and allowing them to refill with bacteria-free water. Exponential doubling times were on the order of a few hours, much more rapid than steady-state doubling times. The methods used in this work may have wider utility in aquatic environments.     

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protien transferase

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella. Correspondence to: R. B. Lingham     

Leishmania promastigotes require opsonic complement to bind to the human leukocyte integrin Mac-1 (CD11b/CD18)

Previous reports have suggested that Leishmania spp. interact with macrophages by binding to Mac-1 (CD1 1b/CD18), a member of the leukocyte integrin family. To better define this interaction, we tested the ability of leishmania promastigotes to bind to purified leukocyte integrins and to cloned integrins expressed in COS cells. We show that leishmania promastigotes bind to cellular or purified Mac-1 but not lymphocyte function-associated antigen-1 in a specific, dose-dependent manner that requires the presence of serum. Binding is inhibited with specific monoclonal antibodies to Mac-1. In the absence of complement opsonization, three different species of leishmania tested fail to bind directly to any of the three leukocyte integrins. We show that binding to Mac-1 requires the third component of complement (C3). Organisms incubated in heat-inactivated serum or serum that has been immunologically depleted of C3 fail to bind to Mac-1. Because the addition of purified C3 to C3-depleted serum restores leishmania binding to Mac-1, we suggest that parasites gain entry into macrophages by fixing complement and subverting a well-characterized adhesive interaction in the immune system between Mac-1 and iC3b.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.