Mechanisms of chromosome banding

A series of biochemical investigations were undertaken to determine the mechanism of Q-banding. The results were as follows: 1. In agreement with previous studies, highly AT-rich DNA, such as poly(dA)-poly(dT), markedly enhanced quinacrine fluorescence while GC containing DNA quenched fluorescence. These effects persisted at DNA concentrations comparable to those in the metaphase chromosome. 2. Studies of quinacrine-DNA complexes in regard to the hypochromism of quinacrine, DNA Tm, DNA viscosity, and equilibrium dialysis, indicated the quinacrine was bound by intercalation with relatively little side binding. 3. Single or double stranded nucleotide polymers, in the form of complete or partial helices, were 1000-fold more effective in quenching than solutions of single nucleotides, suggesting that base stacking is required for quenching. 4. Studies of polymers in the A conformation, such as transfer RNA and DNA-RNA hybrids, indicated that marked base tilting does not affect the ability of nucleic acids to cause quenching or enhancement of quinacrine fluorescence. 5. Salts inhibit the binding of quinacrine to DNA. 6. Spermine, polylysine and polyarginine, which bind in the small groove of DNA, inhibited quinacrine binding and quenching, while histones, which probably bind in the large groove, had little effect. This correlated with the observation that removal of histones with acid has no effect on Q-banding. 7. Mouse liver chromatin was separated into five fractions. At concentrations of quinacrine from 2×10^?6 to 2×10^?5 M all fractions inhibited to varying degrees the ability of the chromatin DNA to bind quinacrine and quench quinacrine fluorescence. At saturating levels of quinacrine two fractions, the 400 g pellet (rich in heterochromatin) and a dispersed euchromatin supernatant fraction, showed a decreased number of binding sites for quinacrine. These two fractions were also the richest in non-histone proteins. 8. DNA isolated from the different fractions all showed identical quenching of quinacrine fluorescence. 9. Mouse GC-rich, mid-band, AT-rich, and satellite DNA, isolated by CsCl and Cs₂SO₄-Ag⁺ centrifugation all showed identical quenching of quinacrine fluorescence, indicating that within a given organism, except for very AT or GC-rich satellites, the variation in base composition is not adequate to explain Q-banding. — We interpret these results to indicate that: (a) quinacrine binds to chromatin by intercalation of the three planar rings with the large group at position 9 lying in the small groove of DNA, (b) most pale staining regions are due to a decrease binding of quinacrine, and (c) this inhibition of binding is predominately due to non-histone proteins.     

Comparison between histones FV and F2a2 of chicken erythrocyte. II. Interaction with homologous DNA.

The conformation and stability of artificial complexes between chicken erythrocyte DNA and homologous histones FV and F2a2 was studied by circular dichroism (CD) and thermal denaturation followed by both absorbance and CD measurements. The complexes are made after a stepwise potassium fluoride gradient dialysis without urea and studied at low ionic strength (10-minus 3 M). 1) No structural changes of the DNA can be detected up to r equals 0.2 with FV and r equals 0.6 for F2a2. With FV at higher values of r the CD spectrum is altered, indicating the organization of DNA and histones in some kind of aggregate. 2) The conformation of histone molecules inside the complexes is not related to the ionic strength of the medium but to an effective ionic environment close to 0.1 M. This ionic strength would also correspond to the melting temperature of histone-covered DNA. 3) From the analysis of the absorbance melting profile the length of DNA covered with an histone molecule can be estimated. A good agreement is found between the negative charge of this piece of DNA and the net positive charge of the histone. 4) Since the CD transition at 227 nm occurs before the second absorbance transition at 280 nm, the DNA is stabilized no longer by native histone but partially or fully denatured histones. The helical regions of the histone molecule are not involved in the binding process, which appears to be almost purely coulombian and most likely related to some structural fit between the pattern of negative charges in the DNA helix and that of positive charges along the peptide chain.     

A Method for Simulating Signal Evolution Using Real Animals

We studied response biases to visual stimulation using a new experimental technique. The subjects (hens, Gallus gallus domesticus) were confronted with several rewarding and non‐rewarding patterns on a computer screen. In contrast with standard discrimination tasks the rewarding patterns were not identical and varied in a dimension differentiating them from the non‐rewarding patterns. The rewarding patterns changed in response to hens' biases in selection of patterns. The aim of the study was to examine the possibility of receivers being a driving force in signal evolution. In one of the experiments a clear‐cut result was obtained. During the course of the experiment the rewarding patterns became gradually more different from the non‐rewarding one, a result expected from theoretical studies of the effect of response bias in signal evolution. A second similar experiment was less conclusive, with ceiling and floor effects influencing the results.     

Nuclear inclusions in the human adenohypophysis. A fine-structural study of nontumorous and adenomatous pituitaries.

Electron microscopy revealed the presence of nonviral nuclear inclusions in human nontumorous as well as adenomatous adenohypophysiocytes, regardless of cell type. Based on ultrastructural appearances, the inclusions have been classified as simple bodies, complex bodies and filamentous aggregates. Many transitional forms were noted between the simple and complex bodies, however, no relationship between the nuclear bodies and filamentous aggregates was found. It can be concluded that the three types of inclusions are normal nuclear constituents. Since no accumulation of these structures was observed in cells associated with enhanced secretion it appears that they are not related to hormonal hyperactivity in the human adenohypophysis.     

Spruce sugars and poultry hydrolysate as growth medium in repeated fed-batch fermentation processes for production of yeast biomass

Bioprocess and Biosystems Engineering - The production of microbial protein in the form of yeast grown on lignocellulosic sugars and nitrogen-rich industrial residues is an attractive approach for...     

Modeling tidal hydrodynamic changes induced by the opening of an artificial inlet within a subtropical mangrove dominated estuary

Wetlands Ecology and Management - The mangrove-estuarine system of Marismas Nacionales, Mexico is considered the most extensive wetland complex of the eastern Pacific coast. Originally, this large...     

Influence of canopy openness,ungulate exclosure,and low‐intensity fire for improved oak regeneration in temperate Europe

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGR_H), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGR_H (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGR_H (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGR_H in burned plots became strongly negative the first year. Thereafter, RGR_H was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.