Radiation damage to dinucleoside monophosphates: mediated versus direct damage

The mediation of radiation-induced damage to dinucleoside monophosphate by oxygen and by glutathione was studied. The sequence isomers d(TpA) and d(ApT) were X-irradiated in aqueous solutions and the products isolated by reverse-phase high-performance liquid chromatography. The main products were characterized by proton NMR spectroscopy. In the presence of oxygen the principal products are the formamido derivative formed by breakdown of thymine and the aldehyde derivative formed at the 5' end of the dinucleoside monophosphate, both nucleoside monophosphates and free bases. In the presence of glutathione, the two stereoisomers of the 5,6-dihydrothymine derivatives are prominent. Radiation-induced damage to d(TpA) and d(ApT) in the solid state was also studied.     

Microscopic and submicroscopic anatomy of the parabronchi, air sacs, and respiratory space of the budgerigar (Melopsittacus undulatus)

The normal microscopic and submicroscopic structure of the lower respiratory tract of the budgerigar (Melopsittacus undulatus) is described and compared with other birds and mammals. Granular (type II) pneumocytes are confined to linings of air sacs, parabronchi, and their atria; however, their secretions (surfactant) cover the surfaces of the infundibula and respiratory space. Infundibula extend from the atria and give rise to the air capillaries, which branch and anastomose freely with those of adjacent infundibula and other parabronchi (interparabronchial septa are not found). Infundibula and the respiratory labyrinth are lined by a continuous epithelium of squamous pneumocytes, whose perikarya are concentrated in the infundibula and whose peripheral cytoplasm is markedly attenuated. The squamous pneumocytes of the respiratory labyrinth share a basal lamina with the blood capillaries that they envelop.     

Synthesis, modification with N-acetoxy-2-acetylaminofluorene and physicochemical studies of DNA model compound d(TACGTA)

The deoxyhexanucleotide d(TACGTA) was synthesized by a modified phosphotriester method. The modified procedure made rapid synthesis of deoxyoligonucleotide possible in gram quantity. N-Acetoxy-2-acetylaminofluorene (AAAF) modified d(TACGTA). Thin layer chromatography and UV analysis of the acid treated AAF modified hexanucleotide showed that the covalent modification with AAF took place exclusively at C(8) of guanine in d(TACGTA). d(TACGTA) and AAF modified d(TACGTA) were purified by preparative high performance liquid chromatography (HPLC). The pure products were characterized by 1H and 31P-NMR. The circular dichroism (CD) spectrum of d(TACGTA) was consistent with DNA in the B form even in the presence of 4 M NaCl whereas the modified hexamer had nearly inverted spectrum in the absence of any added salt. Both NMR and CD analyses indicated profound alteration of conformation of d(TACGTA) upon covalent modification with AAF. The stabilization of the Z-like conformation in the modified hexamer under physiological conditions of salt and temperature suggests biological relevance.     

13C- and 31P-NMR studies of the conformation of carcinogen-modified nucleic acid dimers

The effect of the carcinogen acetylaminofluorene (AAF) on nucleic acid structure was examined using ¹³C- and ³¹P-NMR spectroscopies. Conformational effects were compared in two AAF-modified dinucleoside monophosphates (ApG and GpA) and two AAF-modified deoxydinucleotides (dpApG and dpGpA). Changes in adenine ¹³C chemical shifts on formation of the AAF-adduct and as a function of temperature provided evidence of base stacking. Differences in fluorene ¹³C chemical shifts between the AAF-modified dimer and AAF-modified monomer provided evidence of fluorene stacking. The effect of forming the adduct on the phosphate backbone was examined using ³¹P-NMR. A correlation was demonstrated between the degree of adenine-fluorene stacking on one hand and the change in conformation of the backbone conformation on the other.     

Selection and characterization of transferrin receptor mutants using receptor-specific antibodies

Lymphoma cell lines were selected by growth in transferrin receptor-specific antibodies and in transferrin receptor-specific antibody coupled to ricin toxin. Sequential selections were used to isolate lines with multiple mutations affecting the transferrin receptor molecule. Mutant cell lines were characterized by their growth in antibody and their antibody-binding properties. Two basic types of mutations were found. One type resulted in the loss of a binding determinant for the antibody used for selection on one of the two transferrin receptor allelic products. The other type of mutation resulted in the loss of cell-surface expression of the entire gene product of one of the transferrin receptor alleles.     

Regulation of spvR, the positive regulatory gene of Salmonella plasmid virulence genes

Abstract The regulation of the spvR promoter from the Salmonella dublin virulence plasmid was monitored using proter-reporter gene fusion constructs. Activity was dependent upon the presence of the spv region and was affected by the number of copies of the spv region present with the cell. Activity remained constant throughout exponential growth, and increased rapidly with the onset of stationary phase, under both aerobic and anaerobic conditions. Additionally, the level of spvR expression was controlled by the availability of iron, activity being greatest under low iron conditions in stationary phase. The spvA gene product negatively regulated spvR expression in a dose-dependent manner, indicating that SpvA provides a negative feedback mechanism for this operon.     

Predicting physiognomic vegetation types with climate variables

A quantitative terrestrial vegetation model was produced which consists of:

1. A world classification of important terrestrial plant growth forms (life forms);
2. A set of predictive variables representing the main climatic correlates of these forms; and
3. Empirically obtained hypothetical limiting values defining an ecoclimatic envelope for each plant form (relative to the climatic variables).

The model was applied to a world climatic data-base (1 225 sites) in order to substantiate the hypothesized life-form status of the plant types by accurately predicting their actual world distributions. Particular combinations of forms are interpreted as vegetation formation types by reference to growth-form dominance considerations. Model validation was attempted by comparing predicted and actually occurring vegetation at independent sites on all continents. Prediction accuracy of 85% for individual plant types and 50% for vegetation structure (exact combination of actually occurring dominant forms) suggests that general macroclimatic conditions are much more important than any other factors (such as complex specific interactions) in determining general ecological structure on most sites.     

Experimental transmission of Sarcocystis from icterid birds to sparrows and canaries by sporocysts from the opossum.

Cowbirds (Molothrus ater) and grackles (Cassidix mexicanus) infected with muscle cysts of Sarcocystis were fed to opposums (Didelphis virginiana) and fecal sporocysts from the latter were given to sparrows (Passer domesticus, Family Ploceidae), canaries (Serinus canarius, Family Fringillidae) and ducks (Anas platyrhynchos, Family Anatidae). Asexual parasites were found in the endothelium of sparrows and canaries but not in ducks. When birds were kept 10 weeks or more after infection, muscle cysts were found grossly and microscopically in the majority of sparrows, and in 1 canary, but not in ducks. Muscle zoites were found in digests of all sparrows and canaries but not in that of ducks. Metrocytes and forms dividing by endodyogeny also were found in the digest. Thus, avian Sarcocystis was transmitted experimentally from 2 genera of 1 family (Icteridae) to 2 different families of passerine intermediate hosts by sporocysts from the definitive host. This is the broadest intermediate host spectrum known for a species of Sarcocystis.