NMR study of the structural transition in the DNA-bound water system in the interval of physiological temperatures

Temperature dependence of spin-spin proton relaxation times of DNA and bound water and the content of bound water in the samples of DNA, saturated with water in the atmosphere with different relative humidities from 0 to 100% were studied by means of pulsed NMR. It is shown that the temperature transition in the system of DNA-bound water in the interval 18-35 degrees is observed only when the relative humidity is more than 70% and the double-stranded structure of DNA exists. The transition of DNA from one conformation into another passes through some intermediate state more labile and probably less ordered. This transition is accompanied by changes in the structure of the hydration shell. In the case when relative humidity is greater than 80%, the partial dehydration of DNA stimulated by the transition is observed. This dehydration increases with the increase of relative humidity.     

Activation of the food mutagens IQ and MeIQ by hepatic S9 fractions derived from various species

The ability of hepatic S9 mixes derived from different rodent species (rat, mouse, Syrian and Chinese hamster) to activate the mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) was investigated using Salmonella typhimurium strain TA98. In general, the mutagenicity of IQ and MeIQ was greatest in the presence of S9 fractions from Swiss albino mice and least from fractions derived from Chinese hamsters. However, treatment of rats or hamsters with Aroclor 1254 had little or no effect on the activation of IQ or MeIQ to mutagens.     

Effectiveness of intermittent light treatments on anthocyanin synthesis in dark-grown and light-pretreated seedlings

Differences in the extent of anthocyanin production between intermittent light treatments with short and long dark intervals between successive irradiations are more pronounced in dark-grown than in light-pretreated cabbage seedlings. This observation is consistent with the hypothesis, based on destruction kinetics data, that there might be two pools of phytochrome, a labile one and a stable one, present in different proportions in dark-grown and light-pretreated seedlings, and suggests that light-dependent changes of the stable to labile phytochrome ratio might be physiologically significant in the photoregulation of photomorphogenic responses.     

Heat-induced inhibition of DNA synthesis in L5178Y-S cells is reversed by caffeine

Heating L5178Y cells for 15 min at 43 degrees C caused a decrease in [3H]thymidine incorporation, which could be reversed by post-treatment with 0.75 mM caffeine in an L5178Y-S (radiation-sensitive, heat-resistant) but not in an L5178Y-R (radiation-resistant, heat-sensitive) strain. The reversal was accompanied by a sparing effect of the treatment: survival of L5178Y-S cells increased by a factor of 1.5. The effect of combined (heat + caffeine) treatment of L5178Y-R cells was cumulative.     

On the structure and ecology of the micro-fauna in the Central Amazonian forest stream ‘Igarapé da Cachoeira’

A method was developed to sample the microfauna in open stream water and to observe its food habits over long periods in the laboratory. Evaluation of the material leads to the following conclusions:

1. The microfauna is primarily associated with submerged leaf litter. Its density in the open water is a function of water current and hence, of rainfall,
2. A considerable quantity of living and detritus-biomass is swept down-stream with each heavy rain,
3. The foodweb starts essentially with decomposing fungi and detritus, and to a much lesser extent with algae and bacteria. Protozoa and Rhabdocoela are an insignificant input into the foodweb of higher invertebrates, but their role for maintenance of water quality may be important. Prey of fishes and shrimps depends primarily on ‘primary input’, i.e. on detritus, fungi and to some extent on algae and bacteria. The role of biomass transport from forest streams into larger rivers is discussed in relation to the fauna of the periodically inundated forest (igapó).

     

Radiosensitive Drosophila lines. VIII. The effect of the mus (201)Gl gene of Drosophila melanogaster on the sensitivity of the flies to ultraviolet rays in the imago stage

The effect of UV-light on survival of adult flies of the mutant line mus(2) 201G1 sensitive to methyl methanesulfonate (MMS) was studied. One day old flies were irradiated by UV-light and the survival was determined depending on the UV dose, the genotype and the sex of irradiated flies. High sensitivity of mutant flies was shown in the imaginal stage when division of somatic cells was absent. Moreover, the differences in sensitivity to UV-light were observed depending on the sex of flies. We suggest that the mutation mus(2)201G1 blocking the excision repair affects undivisional cells of the imaginal stage of Drosophila melanogaster.     

Integration of various plasmids into the Bacillus subtilis chromosome

Some features of integration of temperature-sensitive pE194, pGG10 and pGG20 plasmids into the Bacillus subtilis chromosome were studied. Several auxotrophic mutations were obtained using insertion of these plasmids into the chromosome. The sites of plasmids for illegitimate recombination were determined. It was shown that the integration into the Bac. subtilis chromosome is characteristic not only for the plasmid pE194 but is the property of Staphylococcus aureus plasmid pC194 and Escherichia coli pBR322 plasmid. The influence of different Bac. subtilis rec mutations on the frequency of integration was studied.     

Increased superoxide radical production evokes inducible DNA repair in Escherichia coli

Paraquat induced the SOS response in Escherichia coli. This was measured in terms of acquired resistance towards UV lethality in a wild-type strain and in terms of appearance of beta-galactosidase activity in a din::Mu d(Ap lac) fusion strain. However measured, the induction of the SOS response by paraquat was entirely dioxygen-dependent; whereas induction of the SOS response by mitomycin C was independent of the presence of dioxygen. As expected, recA(Def) and lexA(Ind-) isogenic strains did not show the SOS response. It appears likely that O-2, whose intracellular production is increased by paraquat, leads to DNA damage which in turn induces the SOS response.     

A selenomethionine-containing azurin from an auxotroph of Pseudomonas aeruginosa

The production and spectroscopic properties of an L-selenomethionine-containing homolog of Pseudomonas aeruginosa azurin are described. The amino acid substitution was carried out by developing an L-methionine-dependent bacterial strain from a fully functional ATCC culture. Uptake studies monitored using L-[75Se]methionine indicated that L-selenomethionine was incorporated into the protein synthetic pathway of Pseudomonas bacteria in a manner analogous to L-methionine. Several batches of bacteria were grown, and one sample of isolated and purified selenoazurin (azurin in which methionine was substituted by selenomethionine) was found (by neutron activation analysis) to contain 5.2 +/- 0.8 seleniums/copper. Correspondingly, a residual 0.35 methionines, relative to 6.0 in the native protein, were found by amino acid analysis in this azurin sample. The redox potential and extinction coefficient of this selenoazurin were found to be 333 +/- 1 mV (pH 7.0, I = 0.22) and 5855 +/- 160 M-1 cm-1 at 626 +/- 1 nm, respectively. Visible electronic, CD, and EPR spectra are reported and Gaussian curve fitting to the former spectrum allowed assignment of the selenomethionine Se----Cu(II) transition to a band found at 18034 cm-1, based upon an observed 450 cm-1 shift to the red from the analogous band position in the native protein. The data are consistent with a relatively more covalent copper site stabilizing the reduced, Cu(I), form in the selenoprotein. A role for the methionine as a modulator of the blue copper site redox potential by metal----ligand back bonding from Cu(I) is discussed in terms of a ligand sphere which limits the valence change at copper to much less than 1 during a redox cycle.     

Structural characterization of proteoglycans produced by testicular peritubular cells and Sertoli cells

The structural characteristics of proteoglycans produced by seminiferous peritubular cells and by Sertoli cells are defined. Peritubular cells secrete two proteoglycans designated PC I and PC II. PC I is a high molecular mass protein containing chondroitin glycosaminoglycan (GAG) chains (maximum 70 kDa). PC II has a protein core of 45 kDa and also contains chondroitin GAG chains (maximum 70 kDa). Preliminary results imply that PC II may be a degraded or processed form of PC I. A cellular proteoglycan associated with the peritubular cells is described which has properties similar to those of PC I. Sertoli cells secrete two different proteoglycans, designated SC I and SC II. SC I is a large protein containing both chondroitin (maximum 62 kDa) and heparin (maximum 15 kDa) GAG chains. Results obtained suggest that this novel proteoglycan contains both chondroitin and heparin GAG chains bound to the same core protein. SC II has a 50-kDa protein core and contains chondroitin (maximum 25 kDa) GAG chains. A proteoglycan obtained from extracts of Sertoli cells is described which contains heparin (maximum 48 kDa) GAG chains. In addition, Sertoli cells secrete a sulfoprotein, SC III, which is not a proteoglycan. SC III has properties similar to those of a major Sertoli cell-secreted protein previously defined as a dimeric acidic glycoprotein. The stimulation by follicle-stimulating hormone of the incorporation of [35S]SO2(-4) into moieties secreted by Sertoli cells is shown to represent an increased production or sulfation of SC III (i.e. dimeric acidic glycoprotein), and not an increased production or sulfation of proteoglycans. Results are discussed in relation to the possible functions of proteoglycans in the seminiferous tubule.