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Biomedical subjects

D D Brown

Publications and source records attributed to D D Brown.

At least 163 records · Page 9Linked to original sources
PubMed1976

Experimental infections of sheep with Salmonella typhimurium.

Twenty-two-six-to nine-month-old lambs were infected orally with Salmonella typhimurium at levels varying from 2 x 10(13) to 1 x 10(9) and serially slaughtered to determine the pathogenesis of infection and to evaluate the efficacy of diagnostic procedures. Infection resulted in a severe fatal or potentially fatal clinical disease in lambs receiving 2 x 10(13) organisms. Observations were made on the clinical pathology, bacteriology and serology during the course of infection and extensive bacteriological examinations were undertaken at autopsy.

Animals↗
PubMed1976

Experimental infection of poultry with Salmonella infantis.

Six-month-old cockerels and point-of-lay pullets were infected orally with S infantis (1 X 10(10). The cockerels were slaughtered at intervals up to 42 days, and the pullets slaughtered 20 weeks, after infection. Infection produced no clinical disease and minimal changes were observed at autopsy. Serological responses were transient, frequently absent three to six weeks after infection, no response at all being recorded in some birds. Faecal excretion was observed most frequently during the early stages of infection. There was no evidence of egg transmission.

Animals↗
PubMed1975

Brucellosis: a study of five calves from reactor dams.

Five calves from Brucella abortus reactor cows bought after they had been on infected farms for two to six weeks, were reared in isolation and examined serologically for approximately six months prior to cultural and biological examination post mertem. One calf which had been serologically negative to the Rose-Bengal, serum agglutination and complement fixation tests for the last eight weeks of its life yielded a culture of Br abortus biotype 1. This serotype had also been isolated from its dam at parturition.

Agglutination Tests↗
PubMed1975

The size of fibroin messenger RNA and its polyadenylic acid content.

The molecular weight of fibroin messenger RNA has been measured by its contour length in the electron microscope and its electrophoretic mobility under conditions of complete denaturation. These methods give values of 5.6 times 10-6 and 6.0 times 10-6 daltons, respectively. The average molecular weight of 5.8 times 10-6 (1.6 times 10-4 base residues) would be expected to code for a protein of 414,000 daltons, a value about 12 percent larger than the most recently published size for fibroin. When the mRNA is prepared carefully to avoid shear breakage, it is as homogeneous in size as ribosomal RNA. Between 43 percent and 81 percent of the mRNA molecules bind to oligo(dT)-cellulose and are presumed to contain a poly(A) sequence. This sequence, isolated after ribonuclease digestion, comprises about 0.6 percent of the molecule, or an estimated 100 nucleotides. The poly(A) has been localized at the end of the molecule by hybridizing with a small poly (dT:dA) piece and subsequent visualization by electron microscopy. This observation, along with the ability of reverse transcriptase to transcribe fibroin mRNA with an oligo(dT) primer, demonstrates that the poly(A) is at the 3' end of the mRNA.

Adenine Nucleotides↗
PubMed1975

The length of the fibroin gene in the Bombyx mori genome.

Radioactive anti-messenger DNA (3H-cDNA) complementary to silk fibroin mRNA has been synthesized using reverse transcriptase. This 3H-cDNA has been found to be a specific and sensitive probe for the detection of fibroin genes in the genome of Brombyx mori. Actinomycin-CsCl gradients give a large separation of the high GC fibroin genes from the bulk DNA. This density shift of fibroin genes has been measured as a function of DNA molecular weight. The data support a model in which a single high GC fibroin gene of 11.6 times 10-6 daltons is surrounded by at least 6 times 10-7 daltons of low GC DNA (30-39 percent). This finding, along with saturation hybridization studies (Suzuki, Gage, and Brown, 1972), demonstrate that the fibroin gene is present in a single copy per haploid genome.

Animals↗
PubMed1975

Experimental infection of cockerels with Salmonella typhimurium.

Six-month-old SPF Brown Leghorn cockerels were experimentally infected per os with S typhimurium (1 times 1010) and slaughtered at intervals up to 42 days following infection. Observations were made on the clinical pathology, bacteriology and serology during the course of infection and extensive bacteriological examinations were undertaken after post mortem examination.

Administration, Oral↗
PubMed1974

Amplified ribosomal DNA from Xenopus laevis has heterogeneous spacer lengths.

Eco R(1) restriction endonuclease makes two cuts in each repeating unit of amplified ribosomal DNA (rDNA) from Xenopus laevis. The locations of these cuts have been established by comparison of the secondary structure of single-stranded Eco R(1) fragments (as visualized in the electron microscope) with that of X. laevis rRNAs and of long strands of uncut rDNA. Of the two classes of fragments generated, the smaller one contains 90% of the 28S rRNA gene, has a duplex molecular weight of 3.0 x 10(6) and is homogeneous in size. The larger class of molecules contains 80% of the 18S rRNA gene and all of the nontranscribed spacer. These latter fragments are heterogeneous with molecular weights ranging from 4.0 to 5.9 x 10(6). The distribution of sizes within the large class of fragments varies among different preparations of rDNA, and heterogeneity is present in the DNA amplified from the rDNA of a single nucleolar organizer. The heterogeneity is located in the nontranscribed spacer region which is variable in length. This has been demonstrated by the formation of deletion loops in heteroduplexes made between larger fragments of different lengths.

Animals↗