Effect of anti-mosquito antibodies on the infectivity of the rodent malaria parasite Plasmodium berghei to Anopheles farauti

The effect of mouse anti-mosquito antibodies, present in the bloodmeal, on the infectivity of Plasmodium berghei Vincke to Anopheles farauti Laveran was investigated. Significantly fewer oocysts developed in mosquitoes feeding on mice immunized with sugar-fed mosquito midgut antigens than in mosquitoes feeding on control mice. Mosquitoes feeding on mice immunized with the midgut antigens derived from sugar-fed mosquitoes also showed reduced mortality and had lower infection rates than those fed on unimmunized mice. Blood-fed midgut antigen was less effective in producing these effects than sugar-fed midgut antigen.     

Molecular biology of wound-inducible proteinase inhibitors in plants

Abstract. The techniques of molecular biology are being employed to investigate at the gene level the systemically mediated, wound-induced accumulation of two defensive proteinase inhibitor proteins in plant leaves. These techniques have added a new dimension to biochemical and physiological studies already underway to understand the mechanism of induction by wounding. The acquisition of cDNAs from the RNAs coding for the two inhibitors facilitated studies of mRNA synthesis in leaves in response to wounding, and provided probes to obtain wound-inducible proteinase inhibitor genes from tomato ( Lycopersicon esculentum ) and potato (Solarium tuberosum) genomes. Successful transformations of tobacco plants with fused genes, containing the 5' and 3' regions of the inhibitor genes with the open reading frame of the chloramphenicol acelyltransferase ( cat ) gene, have provided a wound-inducible chloramphenicol acetyltransferase (CATase) activity with which to seek cis- and transacting elements that regulate wound-inducibility to help to understand the interaction of cytoplasmic and nuclear components of the intracellular communication systems that activate the proteinase inhibitor genes in response to wounding by insect pests.     

Unusual stability of recombination intermediates made by Escherichia coli RecA protein.

The structure and stability of recombination intermediates made by RecA protein have been investigated following deproteinization. The intermediates consist of two duplex DNA molecules connected by a junction, as visualized by electron microscopy. Although we expected the structures to be highly unstable due to branch migration of the junction, this was not the case. Instead, we found that the intermediates were stable at 37 degrees C. At 56 degrees C, greater than 60% of the intermediates remained after 6 h of incubation. Only at higher temperatures was significant branch migration observed. This unexpected stability suggests that the formation of extensive lengths of heteroduplex DNA in Escherichia coli is likely to require the continued action of proteins, and does not occur via spontaneous branch migration. We show that heteroduplex DNA may be formed in vitro by ATP-dependent strand exchange catalysed by RecA protein or by the RuvA and RuvB proteins of E. coli.     

In vitro development of the hamster and chick secondary palate

A series of experiments were undertaken to compare the in vitro behaviour of the medial edge epithelium (MEE) of hamster, in which palatal shelves normally fuse, and chick, in which they do not fuse. Homotypic pairs of hamster and chick embryo palatal processes, single palatal processes, and heterotypic palatal shelves of both animals were grown in vitro. The results indicated that contact between palatal shelves may not be crucial for MEE differentiation in mammals. The ability to acquire pre-fusion characteristics may be present in mammalian palatal tissue from their early development and may be expressed by cessation of DNA synthesis in the MEE, elevation of cAMP, and MEE cell death. Isolated chick palatal shelf cultured under identical conditions did not express these mammalian pre-fusion characteristics. When MEE of hamster and chick palatal shelves were placed in contact with one another, the intervening epithelia underwent cytolysis. This could be due to either the destruction of chick MEE by lysosomal enzymes liberated from adjacent degenerating hamster MEE cells, or by induction of cell death in chick MEE by hamster mesenchyme. Heterotypic palatal tissue combinations also suggest that release of lysosomal enzymes in the hamster MEE, which leads to its dissolution, may be the terminal event in epithelial differentiation prior to the establishment of mesenchymal continuity. It is suggested that an inverse relationship exists between DNA synthesis and cAMP levels during palatogenesis: when palate closes (as in mammals) the MEE is eliminated by increasing cAMP levels, whereas when palate remains open (as in birds) low level of cAMP preserve the integrity of MEE by supporting DNA synthesis.     

The bactericidal action of beta-lactam antibiotics on an autolysin-deficient strain of Bacillus subtilis

An autolysin-deficient mutant of Bacillus subtilis was completely tolerant to 5 h incubation with 50-100 micrograms cycloserine ml-1 whereas the wild-type was rapidly lysed and killed by 12 micrograms ml-1. Lysis also did not occur when low concentrations of beta-lactams were added to exponentially growing cultures of the mutant, but over 90% of the bacteria were killed within 90-120 min. Protein, lipid and peptidoglycan synthesis as well as growth were inhibited after about 60 min. At this time, but not earlier, small amounts of these three cell components appeared in culture supernatants. Earlier, at about 20-30 min, the intracellular pools of amino acids started to decline rapidly and there was a temporary apparent increase in the rate of lipid synthesis. Neither of the latter phenomena occurred with cycloserine, with which protein and lipid synthesis declined only slowly and the rate of peptidoglycan synthesis was 80% inhibited within 30 min. Only occasional cells with damaged walls were seen 30-90 min after addition of either beta-lactams or cycloserine to the cultures. It thus seems unlikely that wall hydrolysis or penetration by residual autolysins in the mutant are responsible for mass cell death caused by the beta-lactams.     

STUDIES ON EPITHELIAL CELLS ISOLATED FROM GUINEA PIG SMALL INTESTINE

Sheets of mucosal epithelial cells were released from guinea pig small intestine after incubation with ethylenediaminetetraacetate. Cells in sheets retained their columnar shape for 24 hr at room temperature, and exclusion of nigrosine suggested they had intact plasma membranes. When sheets were disaggregated individual cells had normal morphology for at least 4 hr. During isolation 16% of the total protein and 24% of the total lactic dehydrogenase were lost from the cells, but subsequent enzyme leakage was low. Leakage increased with shaking, incubation at 37°C, or increasing the oxygen tension of the suspending medium, but was minimal when the Na⁺:K⁺ ratio in the medium was 8:1 and the osmolarity was high. Losses of particulate enzyme activities were negligible. Respiration was constant for up to 4 hr and was insensitive to calcium, bicarbonate, oxygen tension, and pH. It was inhibited by cyanide and iodoacetate and varied with the Na⁺:K⁺ ratio of the extracellular fluid and the structural integrity of the cells. All preparations concentrated potassium and excluded sodium, but lost this ability if ouabain was added or cells were broken. Potassium-42 uptake was also sensitive to temperature, ouabain, and structural integrity. The preparations are being used to study cell metabolism in the intestinal epithelium.     

吗啡耐受大鼠心房心钠素的释放及其基因转录

本工作应用心钠素放射免疫测定和分子杂交技术首次发现,吗啡耐受大鼠血浆心钠素水平显著降低,心房内心钠素含量明显升高,同时心房内心钠素特异性mRNA水平也相应提高,提示在吗啡耐受时大鼠心房内心钠素的合成和贮存增加,释放减少。     

Production of DON-related trichothecenes byFusarium graminearum Schw from Krasnodarski krai of the USSR

34Fusarium graminearum Schw isolates produced 4-deoxynivalenol to form significant amounts of 4, 7 — dideoxynivalenol and lesser amounts of 4 — deoxynivalenol monoacetates on grain substratesin vitro. This is the first report on the capability a large group of naturally occurring isolates to produce 4,7-dideoxynivalenol. The average levels of 4,7-dideoxynivalenol on rice, corn, barley, and wheat as a substrate were respectively 26.8, 14.0, 12.8, and 10.5% of the level of 4-deoxynivalenol. 4, 7 — dideoxynivalenol was present in all examined naturally contaminated wheat kernel samples at levels of 1.7 to 7.9% of the level of 4-deoxynivalenol. These findings suggest that more attention should be given to the occurrence of 4,7-dideoxynivalenol in cereals.     

Tet(M)-promoted release of tetracycline from ribosomes is GTP dependent.

Tet(M) protein, which displays homology to elongation factor G (EF-G), interacts with the protein biosynthetic machinery to render this process resistant to tetracycline in vivo and in vitro. To clarify the basis of the resistance mechanism, the effects of Tet(M) on several reactions which occur during protein synthesis were examined. The mechanism of action of Tet(M) has been clarified by two observations. The protein relieves tetracycline inhibition of factor-dependent tRNA binding and dramatically reduces the affinity of ribosomes for tetracycline when GTP is present. This reduction in drug affinity appears to be due to a large increase in the rate of tetracycline dissociation. Addition of Tet(M) to ribosome-tetracycline complexes results in displacement of bound drug. And, while Tet(M) and EF-G GTPase activities are tetracycline resistant, the two proteins differ in their sensitivities to fusidic acid, with the latter activity inhibited by the drug. Furthermore, while Tet(M) protects translation from tetracycline inhibition in a defined system, it is unable to substitute for either EF-G or elongation factor Tu.