Multiple arrangements of the human embryonic zeta globin genes.

Rearrangements which are most readily explained by homologous crossover between misaligned segments of DNA in the region of the human embryonic zeta (zeta) globin genes have been identified in individuals of three different racial origins. These recombination events have resulted in a surprisingly high prevalence of chromosomes with single (0.4%) and triplicated (1.3%) zeta genes with apparently no significant effect on the phenotype.     

Sudden large and periodic changes in heart rate in healthy young men after short periods of exercise.

The instantaneous heart rate and respiratory pattern were recorded immediately after brief periods of exercise in 41 healthy male students. Recordings were taken with the subjects both supine and standing. More than half of these subjects showed oscillatory heart changes when recovering supine but not when standing. During these oscillations the heart rate slowed suddenly by more than 30 beats/min; the oscillations had a period of 4 to 8 seconds, and they continued for half to two minutes. The P waves of the electrocardiogram were decreased during the slowing, consistent with increased vagal activity. When these oscillations occurred they each followed the start of an inspiration with the same latency as in respiratory sinus arrhythmia; unlike respiratory sinus arrhythmia, however, they did not occur after every inspiration but varied from 1:1 to 1:3 oscillations:breaths. They were not usually stopped by breath holding but were reduced or abolished by procedures which reduced venous return. This pattern of oscillations--"vagushalt"--seems to be different from respiratory sinus arrhythmias, and central venous pressure may contribute to the phenomenon. Although it is not widely recognised, vagushalt is probably very common and possibly its occurrence may change in disease.     

In vitro influenza virus-specific antibody production in man: antigen-specific and HLA-restricted induction of helper activity mediated by cloned human T lymphocytes

Cloned human T lymphocytes induced with influenza A virus (A/Texas/1/77) and maintained in continuous culture with T cell growth factor were assayed for helper function in the in vitro production of anti-influenza antibody. Helper function mediated by both cloned helper T cells and normal peripheral blood lymphocytes was highly antigen dose-dependent, requiring lower concentrations than that necessary to induce blastogenesis. Optimal help was observed with 1 X 10(2) cloned T cells per culture, whereas excess helper cells inhibited the response. After culture with influenza A virus-induced cloned helper T cells, the antibodies formed were directed against influenza A and not B virus. Furthermore, the cloned helper T cells despite being specific for matrix protein collaborated in the production of predominantly anti-hemagglutinin antibody, suggesting associative recognition of the two discrete antigens. Cellular interactions between cloned helper cells from an HLA-Dw1,3 DR1,3 individual and erythrocyte rosette-negative cells required HLA-Dw1; DR1 compatibility for the production of specific antibody. This was confirmed by using subclones. Finally, it was observed that supernatants of the cloned helper T cells contained functional activity capable of replacing the parent cells in the production of anti-influenza A virus antibody.     

Soil nitrogen mineralisation in a secondary rainforest succession

Summary It has been suggested that soil nitrification is inhibited as a succession develops. This hypothesis was examined in a sub tropical rain forest succession containing five successional stages. Soil mineral nitrogen was measured at the time of collection and after 20 days incubation in the laboratory or field. Sampling was carried out during the wet season and dry season. There was little difference in the ammonium nitrogen concentration at the various sites but increasing amounts of nitrate nitrogen were generally found in each older successional stage.The data show that nitrification inhibition is not an invariable consequence of successional development. Instead the pattern of nitrogen mineralisation is probably related to the overall soil fertility and to the pool of available soil nitrogen.     

A ninth unique influenza virus-coded polypeptide

A polypeptide with a molecular mass of ca. 11 000 has been found in various cell types infected with several strains of influenza A and B viruses. Differences have been found in the electrophoretic mobility of this polypeptide in cells infected with different strains, suggesting that it is virus coded. Peptide mapping studies have shown that this polypeptide is distinct from the eight defined influenza virus gene products. A fraction containing a virus-specific mRNA with an estimated size of ca. 300-400 nucleotides has been obtained. Schemes for the synthesis of this mRNA are discussed.     

Batch- and continuous-culture studies of a methane-utilizing mixed culture

A methane-utilizing mixed culture isolated from activated sludge by selective enrichment at 45°C was found to consist of three interacting species: a methaneutilizing bacterium, a citrate-utilizing bacterium, and a methanol-utilizing bacterium. All three species grew well at 45°C. Three different stable mixed cultures were reconstituted by various combinations of these pure cultures. The nutritional requirements and substrate ranges for each pure culture were determined. The nutritional requirements and substrate ranges for each pure culture were determined. The saturation constant for the methane-utilizing bacterium on methane (K) and for the methanol-utilizing bacterium on methanol (K) were 1.73 × 10^?6M and 4.51 × 10^?7M, respectively. The volumetric mass transfer coefficient for methane (K_L a) was determined to be 65.6 hr^?1.     

Establishment of an in vitro sciarid fly larvae assay to study plant resistance

Mechanisms underlying natural plant resistance to herbivorous invertebrates are still poorly understood in comparison with bacterial or fungal interactions. One reason is the difficulty in reliably and reproducibly assessing the effects under controlled conditions. This article describes a newly developed in vitro biological assay system that enables the interactions between sciarid larvae and plants, whose roots they feed on, to be studied under highly controlled conditions. The bioassay eliminates the problems created by the often variable environmental factors by providing an aseptic arena where experimental plants can be germinated and grown on agar within a Petri dish. Sciarid fly eggs are then collected, sterilised and added to the Petri dish. The system allows the eggs to hatch and the larvae to feed on the plant roots. A range of developmental parameters can then be recorded over time which can then be correlated with the experimental plant type. This assay system also allows a simultaneous comparison or 'choice chamber' between two (or more) different genotypes. The assay should greatly help to facilitate the identification of new components involved in insect resistance mediated pathway via the characterisation of mutant plants.     

Inhibition of co-operative enzymes by substrate-analogues: Possible implications for the physiological significance of negative co-operativity illustrated by phenylalanine metabolism in higher plants

The “Hill” equation for co-operative binding-systems has been extended to describe the effect of substrate-analogue on the binding of substrate to an oligomeric protein. It is demonstrated that the more negatively co-operative the binding-system, the more sensitive is the binding of substrate to inhibition by increases in the relative concentration of substrate-analogue. It is proposed that the physiological significance of negative co-operativity for enzymes may be complementary to the physiological significance of positive co-operativity. The effect of negative co-operativity is to make substrate binding more sensitive to inhibition by relative increases in the concentration of substrate-analogue (e.g. for many enzymes product of the reaction) at the expense of decreased sensitivity of substrate binding to relative changes in substrate concentration compared to a system with equivalent, independent substrate binding sites. In contrast, the effect of positive co-operativity is to make the enzyme more sensitive to relative changes in substrate concentration at the expense of decreased sensitivity to inhibition by relative increases in product concentration, compared to an enzyme without co-operative binding.