Divergence, differential methylation and interspersion of melon satellite DNA sequences.

Melon (Cucumis melo) satellite DNA consists of two components, Q and S, each with a buoyant density in CsCl of 1.707 g/ml, but differing by 9 degrees C in "melting" temperature. These physical properties appear to be in contradiction, since both depend on G + C content. In order to resolve this anomaly, base compositions were directly determined for isolated fractions. the low-"melting" component S contains 41.8% G + C, with 6% of C present as 5-methylcytosine, whereas Q DNA contains 54% G + C, with 41% of C methylated. Analyses of restriction site loss agreed well with the direct determinations of methylation and divergence, and indicated some clustering of methylated sites in Q DNA. Analysis of restricted main-band DNA by hydridization with RNA complementary to Q satellite DNA ("Southern transfer") showed satellite Q tandem arrays interspersed in DNA of main-band density. Sequence divergence and extent of methylation did not appear to depend on whether a repeat array was present as satellite or interspersed in main-band DNA. Hydridization in situ indicated considerable heterogeneity in the genomic proportion of the Q-DNA sequences in melon fruit nuclei, implying over- and under-representation consistent with extensive unequal recombination in satellite Q tandem arrays. The cucumber, Cucumis sativus, contains less than 8% as much Q-homologous DNA per genome as the melon, suggesting rapid evolutionary gain or loss of these tandem repeat sequences.     

Further observations on cell wall morphogenesis and polysaccharide arrangement during plant growth

Summary The three-dimensional arrangement of the polysaccharide chains in cell walls was investigated, using ultracryotomy and cytochemistry, in order to test the validity of the previously postulated ordered fibril hypothesis and to analyze the characteristics of the primary wall morphogenesis.Both in mung bean hypocotyl (Phaseolus aureus) and pea root (Pisum sativum) cultured in defined conditions, cell to cell endogenous specificity is marked by differences in the numbers of layers, thickness, rhythm and direction of deposition. The occurrence of bow-shaped arrangements and of strata of orientation intermediate between the main crisscrossed multifibrillar layers suggests that the sequential changes of the morphogenetic activity of the cells is progressive. The twisted polysaccharide disposition evokes certain mesomorphic states; a part of the mechanism responsible for the wall arrangement may result from a self-assembly process as in the orientation of the molecules in a liquid cristal. This possibility finds experimental support in the fact that a three-dimensional association of the hemicellulose chains spontaneously appears when precipitated in acellular conditions.Polysaccharide removal associated with shadowing indicates that the ordered disposition within the wall is extensively altered by even a slight extraction. These data may invalidate diverse results which are generally brought forward to explain the wall organization during growth.     

Effect of hydrogen sulfide on growth of sulfate reducing bacteria

A culture of sulfate reducing bacteria (SRB) growing on lactate and sulfate was incubated at different pH values in the range of 5.8-7.0. The effect of pH on growth rate was determined in this pH range; the highest growth rate was observed at pH 6.7. Hydrogen sulfide produced from sulfate reduction was found to have a direct and reversible toxicity effect on the SRB. A hydrogen sulfide Concentration of 547 mg/L (16.1 mM) completely inhibited the culture growth. Comparison between acetic acid and hydrogen sulfide inhibition is presented and the concomitant inhibition kinetics are mathematically described. (c) 1992 John Wiley & Sons, Inc.     

A universal primer mixture for sequence determination at the 3′ ends of cDNAs

We have devised a universal primer which can be used to sequence the 3′-ends of cloned cDNAs containing a polyA tail. The primer consists of an equimolar mixture of three primers: 20 T nucleotides followed by either an A, C, or G nucleotide (5′→3′). With this primer mixture and the dideoxynucleotide chain termination method, we determined the 3′-terminal sequence of human β-actin cDNA in an Okayama-Berg vector, in four parallel sets of reactions containing either a single primer (T₂₀G, T₂₀C, or T₂₀A) or an equimolar mixture of all three primers. Priming with both T₂₀A and the triple mixture gave clearly readable results that agree with the known sequence of the human β-actin gene, and we have applied this method successfully to several other cDNAs in the Okayama-Berg expression vector. Use of this universal primer mixture facilitates determination of sequences at the 3′-ends of cDNAs while by-passing the polyA tail region.     

Interclonal variation in methylation patterns for expressed and non-expressed genes.

A mass culture of human diploid fibroblasts, and eight clones isolated from that mass culture, were examined for methylation patterns in several regions of DNA. Plasmid-inserted cDNA sequences were used as probes for alpha-hCG, beta-globin, A gamma- and G gamma-globin, and beta- and gamma-actin gene regions. Each probe revealed a different clone-specific pattern of DNA methylation, indicating a striking degree of inter-clonal heterogeneity, for those gene regions which are not normally expressed in diploid fibroblasts (alpha-hCG, gamma-globin and beta-globin). Intra-clonal variation was also evident in many instances, implying that heterogeneity could arise de novo in pure cell clones during serial passage. Thus methylation patterns, in particular for repressed genes, appear to be unstably inherited in these cells, and this instability may lead to random derepression in some cell lineages during mitotic growth.     

Electrophysiology of phagocytic membranes. II. Membrane potential and induction of slow hyperpolarizations in activated macrophages.

The potential differences measured on the cell surface and after penetration into the cytoplasm of activated macrophages are described. Linear regressions are made of the measured potential differences as functions of the tip potential of each microelectrode. The surface potential of the macrophage is not significantly different from zero. Mouse macrophages have a transmembrane potential of--26 mV, whereas in guinea-pig cells this value is--18 mV. The input resistances of guinea-pig cells are higher than those of mouse macrophages. The cytoplasmic location of the electrode was characterized both by fluorescent dye injection and by electric criteria. Slow membrane hyperpolarizations are directly elicited by mechanical stimulation. Electric responses evoked by current pulses were further characterized. Our results lead to the extablishment of objective criteria to validate intracellular recordings from macrophage.     

Fate of mimosine administered orally to sheep and its effectiveness as a defleecing agent.

Mimosine was administered orally to Merino sheep once daily for periods of 1-3 days, either as the isolated compound or in the foliage of Leucaena leucocephala. A single daily dose of mimosine of 450 or 600 mg/kg body weight was effective for defleecing sheep. A daily dose rate of 300 mg/kg was effective for defleecing sheep if given on two successive days. The effectiveness of a treatment for defleecing sheep was related to the concentration of mimosine in plasma following dosing; defleecing ensued when the concentration of mimosine in plasma was maintained above 0-1 mmol/l for at least 30 h. The main products excreted in urine were mimosine and 3,4-dihydroxypyridine (DHP); small amounts of mimosinamine were also excreted. During the first day following dosing, the major excretory product was mimosine; DHP was an important component during the second and third days. In the three days following the start of dosing, between 32 and 53% of the mimosine given was accounted for as mimosine in the urine. Following an intravenous infusion of mimosine, no DHP was detected in urine; most of the mimosine was excreted intact but a small amount (c. 9%) was excreted as mimosinamine.     

Enhanced production of human gamma-interferon in nylon column-fractionated cell cultures

The production of human gamma-interferon (HuIFN-gamma) in unfractionated and nylon wool column-fractionated leukocyte cell cultures stimulated with PMA and PHA was investigated. Production was studied with normal and reduced autologous serum protein levels in 96-hr spinner cultures. A 10- to 15-fold enhancement of production and a 50-fold increase in specific activity of crude HuIFN-gamma was demonstrated in nylon column-fractionated/reduced serum cell cultures. Kinetic analysis revealed a production rate maximum within 6 hr of induction in unprocessed cell cultures, whereas production occurred at an essentially constant rate for 48 hr in fractionated cell cultures.     

Breeding biology of White‐rumped Tanagers in central Brazil

ABSTRACT White‐rumped Tanagers (Cypsnagra hirundinacea) are widely distributed in northern Brazil, Bolivia, and Paraguay, and are classified as vulnerable in the state of Paraná and as endangered in the state of São Paulo, Brazil. Little is currently known about their breeding biology. We studied the breeding behavior of White‐rumped Tanagers in the Cerrado (Neotropical savanna) in central Brazil from 2002 to 2007. The breeding period extended from mid‐August to mid‐December. Nests were cup‐shaped and located mainly in trees of the genus Kielmeyera at a mean height of 3.7 ± 0.3 m (SE). Clutch sizes varied from one to three eggs and the incubation period lasted an average of 16.0 ± 0.3 d. Incubation was by females only and started with the laying of the first egg. Mean nest attentiveness (percent time on nests by females) was 64 ± 0.08%. Nestlings were fed by males, females, and, when present, helpers. The mean rate of food delivery rate to nests was 5.2 ± 0.4 items/h, with rates similar for males (mean = 2.7 ± 0.3 items/h) and females (mean = 2.4 ± 0.3 items/h). The mean duration of the nestling period was 12.1 ± 0.5 d. Compared to many temperate species of tanagers, White‐rumped Tanagers in our study had relatively small clutches, low nest attentiveness, and long incubation periods. As with other tropical species, such characteristics might be due to food limitation or high rates of nest predation.