The influence of single-strand breaks on the kinetics of denaturation of DNA

The influence of single-strand breaks on the kinetics of the relaxation of DNA in a solution of low ionic strength has been investigated by a temperature jump method. The relaxation of DNA after a jump of 0.7 °C in the melting region has been monitored by measuring the extinction at 260 nm. For essentially monodisperse T4 DNA (M = 130 × 10⁶) two distinct relaxation times have been observed, that depend markedly on the initial extent of denaturation 1 ? θ. The larger relaxation time decreases from 450 sec to about 300 sec, the smaller one from 55 see to 30 when 1 ? θ increases from 0.03 to about 0.8. The dependence of these relaxation times on the average number of single-strand breaks per molecule (p) appears to be very small up to p = 100. However, the relative contribution of the slow process decreases sharply when p increases from 0.6 to 30 and remains nearly constant for larger p. The observations are discussed in the light recent theories of the kinetics of denaturation.     

Transient electric birefringence of T-even bacteriophages. II. T4B in the presence of tryptophan and T4D.

Measurements of electric birefringence, sedimentation velocity, and biological adsorption rate are used to study the properties of bacteriophage T4B in the presence of excess tryptophan. The adsorption rate determined in borate buffer pH 9 (at 25°C) increases from 0.003 × 10^?8 ml min^?1 (0.025 M) to 0.130 × 10^?8 ml min^?1 (0.150 M). The Kerr coefficient, rotational diffusion coefficient, and the sedimentation coefficient of the phage are also dependent on buffer concentration and reach plateau values above 0.12 M given by K_sp = ?(275 ± 18) × 10^?9 OD^?1 cm² statvolt^?2, D_25,w = 133 ± 4 sec^?1, and s_20,w = 818 ± 11 S. From a comparison of electric birefringence measurements of T4B and T4D it is concluded that T4D and T4B (in the presence of excess tryptophan) exhibit a similar hydrodynamic behavior. The change in physical parameters is solely due to a shift in fiber configuration. At high buffer concentrations the fibers make an angle of approximately 3π/4 with the sheath and the permanent dipole moment is about 200,000 D. This dipole moment is roughly ten times as large as that of a phage particle with nonextended fibers. This difference may be due to a change in hydrodynamic center upon fiber extension or to the presence of positive charges on the fiber tips, or both. At intermediate buffer concentrations the phage population behaves as if it were monodisperse. Probably not all six fibers are extended under such conditions.     

Endocytosis in absorptive cells of cultured human small-intestinal tissue: Effect of cytochalasin B and D

Summary The effect of cytochalasin B (CB) and cytochalasin D (CD) on the endocytotic uptake of horseradish peroxidase (HRP) by intestinal absorptive cells was investigated by morphometric methods. The results showed that CD inhibited endocytosis considerably, and without any detrimental side-effects. CB had hardly any effect on the endocytosis of HRP, but caused a significant decrease in the number of apical vesicles and tubules involved in the transport of cell-coat glycoproteins from the Golgi apparatus to the brush border.Electron-microscopic autoradiographic analysis of the effect of CD showed that although endocytosis is inhibited significantly by the drug, the amount of radiolabelled cell-coat material entering the lysosome-like bodies was unaltered compared with control cultures. These observations support our hypothesis that the cell-coat glycoproteins of the absorptive cells enter the lysosome-like bodies by a crinophagic rather than by an exocytotic-endocytotic mechanism.     

Comparison of British populations of potato cyst nematodes with populations from continental Europe and South America using RAPDs.

Genetic variation between populations of Globodera pallida, primarily from Britain but including populations from continental Europe and South America and two Globodera rostochiensis populations, was examined using random amplified polymorphic DNA (RAPD). Fourteen primers were used and 250 amplification products observed. A comparison was made of the similarities between the species and, within G. pallida, between populations from Britain, The Netherlands, Germany, and Switzerland, of the pathotypes Pa2 and Pa3. In addition, one Pa1 population and two others from South America were included. On the basis of the RAPD analysis, all the Pa2-Pa3 populations, except one from Scotland (Luffness), constituted a single group with no clear distinction based on pathotype designation. The Luffness population is known to be distinct in its virulence. The data indicated that the main Pa2-Pa3 group could be subdivided based on geographic origin, but this is not well supported by bootstrap analysis. The Pa1 population and the two populations from South America all formed distinct groups.     

Site-Dependent Life-Cycle Impact Assessment of Acidification

The lack of spatial differentiation in current life-cycle impact assessment (LCIA) affects the relevance of the assessed impact. This article first describes a framework for constructing factors relating the region of emission to the acidifying impact on its deposition areas. Next, these factors are established for 44 European regions with the help of the RAINS model, an integrated assessment model that combines information on regional emission levels with information on long-range atmospheric transport to estimate patterns of deposition and concentration for comparison with critical loads and thresholds for acidification, eutrophication via air; and tropospheric ozone formation. The application of the acidification factors in LCIA is very straightforward. The only additional data required, the geographical site of the emission, is generally provided by current life-cycle inventory analysis. The acidification factors add resolving power of a factor of 1,000 difference between the highest and lowest ratings, while the combined uncertainties in the RAINS model are canceled out to a large extent in the acidification factors as a result of the large number of ecosystems they cover The framework presented is also suitable for establishing similar factors for eutrophication and tropospheric ozone formation for regions outside Europe as well.     

Biological Control of Fusarium oxysporum f.sp. asparagi by Applying Non-pathogenic Isolates of F . oxysporum

Root rot severity of asparagus plants grown in sterilized field soil inoculated with Fusarium oxysporum f . sp . asparagi (Foa) was reduced by more than 50% when the soil was precolo nized by each of 13 non - pathogenic (np) isolates of F. oxysporum originating from asparagus roots or field soils . In a greenhouse experiment , application of six np isolates to naturally infested field soil was followed by a 23 - 49% decrease of disease severity , depending on the isolate . One of them , Fo47 originating from Fusarium suppressive soil in France , was applied to field plots infested with Foa . Foa root rot was not suppressed in asparagus plants grown for 1 year in these plots . Pathogenic and np isolates extensively colonized the root surface and isolates of both types infected the roots of asparagus plants grown in sterilized field soil , with significant differences among the np isolates . Inoculation of sterilized field soil with np isolates reduced germination of Foa chlamydospores by 43 - 64% depending on the isolate used . It is concluded that np isolates of F. oxysporum can suppress asparagus root rot caused by Foa in naturally infested field soil . The differences for root colonization capacity among the np isolates imply that selection for this trait might reveal isolates that perform better under field conditions .     

Effect of Age-Stiffening Tissues and Intraocular Pressure on Optic Nerve Damages

Age-stiffening of ocular tissues is statistically linked to glaucoma in the elderly. In this study, the effects of age-stiffening on the lamina cribrosa, the primary site of glaucomatous nerve damages, were modeled using computational finite element analysis. We showed that glaucomatous nerve damages and peripheral vision loss behavior can be phenomenologically modeled by shear-based damage criterion. Using this damage criterion, the potential vision loss for 30 years old with mild hypertension of 25mmHg intraocular pressure (IOP) was estimated to be 4%. When the IOP was elevated to 35mmHg, the potential vision loss rose to 45%; and age-stiffening from 35 to 60 years old increased the potential vision loss to 52%. These results showed that while IOP plays a central role in glaucomatous damages, age-stiffening facilitates glaucomatous damages and may be the principal factor that resulted in a higher rate of glaucoma in the elderly than the general population.     

Helminths of saiga antelope in Kazakhstan: implications for conservation and livestock production

Saiga antelope (Saiga tatarica) graze extensively on livestock pasture, potentially enabling transmission of a wide range of parasitic helminths between saigas and domestic ruminants. Thirty-six of the 38 species of helminth that have been found in saigas in Kazakhstan in the past have been found also in domestic livestock. We examined 133 saigas culled for meat in autumn 1997, and found three species of cestode and 12 nematodes (nine in the abomasum), but no trematodes or lungworms. The most abundant species were Marshallagia marshalli, Marshallagia mongolica, and Nematodirus gazellae in the abomasum, Nematodirus gazellae in the small intestine, and Skrjabinema ovis in the large intestine. There was no clear relationship between intensities of abomasal nematodes and body condition. Age-intensity patterns differed between species: N. gazellae intensities were highest in saigas around 2-3 yr old, and declined in older animals, whereas the intensity of Marshallagia spp. rose asymptotically with age. Fecal egg density was directly proportional to adult worm intensity across ages for Marshallagia spp., but only in young animals for N. gazellae. There was no evidence that helminths, at the intensities observed, adversely affect saiga populations. The host range of many of the parasites found is broad, and transmission between saigas and livestock in both directions might become important to agriculture and conservation as livestock numbers recover. Simplified sampling techniques used in this study, and statistical analysis based on bootstrapping, could prove useful in other parasitologic surveys of wildlife in remote areas.