On a simplified model of the renal medulla.

A set of equations that approximate the central core model of the human kidney are solved. It is noted that the solution indicates a limit to the increase in solute concentration in the descending limb of Henle for a given metabolic pump term. Comparison is made with the results of an alternative theory, and numerical results are presented for the increase in solute concentration in the descending limb of Henle.     

HIV infection among women undergoing abortion in Montreal.

OBJECTIVE: To determine the seroprevalence and correlates of HIV infection in a subpopulation of women of childbearing age in Montreal. DESIGN: Anonymous unlinked seroprevalence study. SETTING: Pregnancy termination unit in a teaching hospital in Montreal. PARTICIPANTS: Women presenting for abortion from July 1989 to June 1993 who resided in Quebec and were not known to have HIV infection; 12,017 (99.6%) of 12,068 eligible women were included in the study. INTERVENTION: HIV antibody testing of serum left over from samples obtained for routine Rh typing; the same algorithm as for serodiagnostic testing, namely enzyme immunoassay (EIA) followed by confirmatory testing of repeatedly EIA-reactive samples, was used. OUTCOME MEASURES: HIV serostatus by age, marital status, region of residence (metropolitan Montreal versus other), country of birth and number of living children. RESULTS: Most (84.7%) of the subjects resided in metropolitan Montreal. The median age was 27.0 (range 13 to 50) years. The serum samples of 22 women were confirmed to be HIV positive, for an overall seroprevalence rate of 1.8 per 1000 (95% confidence interval 1.1 to 2.8). The seroprevalence rate did not vary significantly by age, marital status, region of residence or study year. However, it was strongly correlated with country of birth: Canada 0.16, Haiti 23.5, HIV-endemic countries other than Haiti 5.3 and non-HIV-endemic countries other than Canada 0.0 per 1000. The seroprevalence rate among women born in Haiti was 147 times higher than that among women born in Canada (p < 0.0001). Of the women born in Haiti the rate was 3.0 times greater among those who immigrated to Canada in 1985 or later than among those who immigrated earlier (p = 0.047). CONCLUSIONS: The results of this study indicate that the HIV seroprevalence rate among women in Montreal is strongly associated with country of birth, women born in HIV-endemic countries, especially Haiti, having the highest rate. These results will help in the development of policies regarding HIV antibody testing and prevention of HIV transmission in Quebec.     

Effects of Substituting Granulin or a Granulin-Polyhedrin Chimera for Polyhedrin on Virion Occlusion and Polyhedral Morphology in Autographa californica Multinucleocapsid Nuclear Polyhedrosis Virus

Substitution of granulin from the Trichoplusia ni granulosis virus (TnGV) for polyhedrin of the Autographa californica multinucleocapsid nuclear polyhedrosis virus (AcMNPV) yielded a few very large (2 to 5 μm) cuboidal inclusions in the cytoplasm and nucleus of infected cells. These polyhedra lacked the beveled edges characteristic of wild-type AcMNPV polyhedra, contained fractures, and occluded few virions. Placing a nuclear localization signal (KRKK) in granulin directed more granulin to the nucleus and resulted in more structurally uniform cuboidal inclusions in which no virions were observed. A granulin-polyhedrin chimera produced tetrahedral occlusions with more virions than granulin inclusions but many fewer than wild-type polyhedra. Despite the unusual structure of the granulin and granulin-polyhedrin inclusions, they interacted with AcMNPV p10 fibrillar structures and electron-dense spacers that are precursors of the polyhedral calyx. The change in inclusion shape obtained with the granulin-polyhedrin chimera demonstrates that the primary amino acid sequence affects occlusion body shape, but the large cuboidal inclusions formed by granulin indicate that the amino acid sequence is not the only determinant. The failure of granulin or the granulin-polyhedrin chimera to properly occlude AcMNPV virions suggests that specific interactions occur between polyhedrin and other viral proteins which facilitate normal virion occlusion and occlusion body assembly and shape in baculoviruses.     

Specificity of interplant cycling of phosphorus: The role of mycorrhizas

The cycling of nutrients from dying roots of one plant (the donor) to other intact plants (the receivers) was examined in a series of pot experiments. In each pot receiver plants formed either the same or a different type of mycorrhiza as the donor plant and was therefore respectively either capable or incapable of forming mycorrhizal hyphal links to the donor. There was a preferential transfer of ³²P from the dying roots of the vesicular-arbuscular mycorrhizal (VAM) Lolium perenne to VAM-infected trees Acer pseudoplatanus and Fraxinus excelsior compared to the ectomycorrhizal (ECM) Larix eurolepis, this despite an apparently greater competitive ability of L. eurolepis to obtain ³²P from the soil. Following the death of L. perenne roots there was also an increase in total P in the VAM tree receiver. These findings could not be explained by similarities in rooting distribution of the VAM-infected plants.In a similar study of the transfer of ³²P between heathland plants there was a preferential cycling of ³²P from one ericoid mycorrhizal Calluna vulgaris to another rather than to the VAM Molinia caerulea. In contrast, when ³²P was supplied directly to the soil, M. caerulea obtained significantly more ³²P than C. vulgaris. These results are discussed in relation to the potential role of interplant mycorrhizal links in the cycling of nutrients within partially closed cycles and the implications that this might have for species balance in plant communities.     

18S coding sequences in amplified ribosomal DNA from Xenopus laevis oocytes are highly homogeneous, unmethylated, and lack major open reading frames.

We have used two approaches to search for sequence variants in the 18S coding region of amplified ribosomal DNA (rDNA) from Xenopus laevis oocytes. First, using clones derived from amplified rDNA, we compared the equivalent of a complete 18S coding region from two clones and short regions from two other clones with the 18S sequence previously determined from a "reference" clone. The respective sequences in all the clones were identical. Secondly, we examined greater than 60% of the 18S sequence in "pooled 18S genes" in uncloned amplified rDNA. The predominant sequence corresponded to that in the reference clone and no heterogeneities were apparent. Since many chromosomal rDNA units contribute to rDNA amplification the findings indicate that 18S coding sequences in X. laevis are largely homogeneous. The previously established sequence is the predominant one, thus providing a reliable basis for studies on 18S rRNA. Sequencing gels on uncloned amplified rDNA confirmed the absence of methylated cytosine in this DNA. The 18S sequence lacks major open reading frames.     

Nucleoprotein Complexes in Simian Virus 40-Infected Cells

When African green monkey kidney cells (BSC-1) were infected with simian virus 40 (SV40) and extracted with 0.25% Triton X-100 after exposure to (3)H-thymidine, the (3)H-SV40 deoxyribonucleic acid (DNA) was present in a form which had a sedimentation coefficient in sucrose gradients of 44S. The change from the sedimentation coefficient of purified SV40 DNA (21S) was shown to result from the association of the SV40 DNA in the Triton extracts with protein by means of sensitivity to Pronase digestion and labeling with (14)C-amino acids. Short-term labeling experiments with (3)H-thymidine demonstrated that SV40 DNA molecules in the course of replication (25S) were also present as nucleoprotein complexes in Triton-extracted material. Labeled DNA extracted with Triton in the form of nucleoprotein complexes was obtained in amounts which were quantitatively equivalent to the amounts extracted with deoxycholate in parallel experiments. This indicated that the newly synthesized pools of SV40 DNA may not occur as free DNA in the infected cell.     

Superhelix Density Heterogeneity of Intracellular Simian Virus 40 Deoxyribonucleic Acid

Covalently closed intracellular and viral simian virus 40 (SV40) deoxyribonucleic acid (DNA) were separately isolated from infected African green monkey cells (BSC-1) grown in culture. The two DNA species form overlapping bands centered at different positions in a propidium di-iodide-cesium chloride (PDI-CsCl) buoyant density gradient capable of separating closed DNA species with different superhelix densities. When the dense side of a (32)P-labeled intracellular DNA band was mixed with the light side of a (3)H-labeled intracellular DNA band and again centrifuged in a PDI-CsCl density gradient, two overlapping bands formed with modes displaced from each other. Similar band-splitting experiments performed with viral DNA always gave superimposable bands. The foregoing experiments demonstrate that the intracellular DNA is heterogeneous in superhelix density, whereas, by the same criteria, the viral DNA is homogeneous. The mean superhelix density of the intracellular closed DNA is approximately three-fourths as large as the superhelix density of the viral DNA. These results rule out the possibility that closed SV40 DNA is drawn randomly from the intracellular pool and assembled without a further nicking-closing step into virions. When the cells were grown and infected in the presence of ethidium bromide (EB), the intracellular closed DNA was found to be homogeneous in superhelix density and to have the same superhelix density as the viral DNA which, in turn, was unaffected by the presence of the drug. The foregoing results were explained by postulating that the intracellular DNA is formed with a homogeneous superhelix density and becomes heterogeneous in the absence of EB as a result of a nicking-closing cycle that occurs in a spacially or temporally heterogeneous environment. The drug EB would inhibit this action by inhibiting the nicking enzyme(s).     

A comparative study of the extracellular and cell-wall polysaccharides of someCandida species

Candida bogoriensis, C.buffonii, C.diffluens, C.foliarum andC.javanica, produce an extracellular polysaccharide which contains galactose, glucose, mannose, fucose and rhamnose. These sugars were also found in cell-wall preparations of the same yeast species. The cell-wall preparations ofC.diffluens andC.foliarum included capsular material. The similarity in composition of the extracellular polysaccharides and components of the cell wall suggests that both are synthetized by the same enzymatic system. The fiveCandida species may be closely related.