The Aedes aegypti genome: complexity and organization.

We describe the use of DNA reassociation kinetics to determine the total genome size and complexity together with the individual complexity and copy number of the single copy, middle repetitive and highly repeated DNA fractions of cell line and larval DNA from the mosquito, Aedes aegypti. The genome of Ae. aegypti is both large and complex, being one third the size of the human genome, and exhibits a short period interspersed repeat pattern. The implications of patterns of sequence arrangement and genome complexities for experiments aimed at isolating specific classes of DNA sequences, such as mobile genetic elements, are discussed.     

Ochratoxin A-induced iron deficiency anemia.

Ochratoxin A at 8 micrograms per g of diet, but not at lower doses, fed to chickens from 1 day to 3 weeks of age resulted in significantly (P less than 0.05) decreased packed blood cell volume and hemoglobin concentration without altering the number of circulating erythrocytes. Serum iron and percentage of transferrin saturation were lowered at 4 and 8 micrograms/g. Therefore, anemia was characteristic of severe ochratoxicosis of young chickens, and the anemia was categorized as a hypochromic-microcytic anemia of the iron deficiency type. These data indicate that ochratoxin A by itself does not cause hemorrhagic anemia syndrome of chickens and that an anemia caused by a nutritional deficiency can be elicited by a mycotoxin.     

Urease catalysis and structure: X. Alternate bonding-site isozymes of jackbean urease

Three previously uncharacterized, nongenetic urease isozymes have been analyzed by sucrose density gradient sedimentation, gel electrophoresis, and chemical reactivity. The full complement of isozymes could be reliably generated by choosing appropriate levels of NaCl, pH, and ethylene glycol, and was stable for several days in dilute solution. The three forms of interest were found to be quaternary isomers of other isozymes, but differed from them qualitatively in their bonding sites, with disulfide bonds being substituted for noncovalent bonds. The separation of these isomer-pairs during sedimentation and electrophoresis cannot be readily explained by differences in size or charge, but must rather arise from a difference in shape. A simple two-dimensional model can provide the appropriate molecular architecture to satisfy these requirements: Only one of the two half-units in each α-urease molecule undergoes disulfide bonding during polymerization, and it does so with two adjacent molecules, thus producing asymmetric polymers from symmetric starting components.     

Studies on the mechanism of suppression of delayed hypersensitivity by the antischistosomal compund niridazole.

Niridazole given in a single oral dose of 100 mg/kg to guinea pigs sensitized to ortho-chlorobenzoyl chloride-bovine gamma-globulin (OCB-BGG) regularly abolished delayed cutaneous reactivity. Little effect was observed, however, when cells from these animals were tested in vitro with either direct or indirect assays for migration inhibitory factor (MIF). On the other hand, sera taken from nonsensitized guinea pigs after they had received 100 mg/kg of niridazole markedly diminished antigen-induced inhibition of migration of sensitized peritoneal exudate cells in vitro. The immunosuppressive effects of such sera could not be produced by niridazole itself, thereby suggesting an effect of niridazole metabolites. This suppressive activity was readily removed from the serum by dialysis. The active serum blocked the production of MIF by sensitized lymph node cells but did not affect the action of preformed MIF on macrophages. The effect of this serum was reversible; lymph node cells incubated for 24 hr with active serum, then washed and reincubated with antigen in normal serum, produced normal amounts of MIF. These studies suggest that metabolites of niridazole, but not the parent compound itslef, suppress delayed hypersensitivity in guinea pigs and prevent MIF production by lymphocytes without affecting the macrophage response to MIF.     

Sequence-based genetic markers for genes and gene families: single-strand conformational polymorphisms for the fatty acid synthesis genes of Cuphea

 Gene sequences are rapidly accumulating for many commercially and scientifically important plants. These resources create the basis for developing sequence-based markers for mapping and tracking known (candidate) genes, thereby increasing the utility of genetic maps. Members of most of the gene families underlying the synthesis of seed oil fatty acids have been cloned from the medium-chain oilseed Cuphea. Allele-specific-PCR (AS-PCR) and single-strand conformational polymorphism (SSCP) markers were developed for 22 fatty acid synthesis genes belonging to seven gene families of Cuphea using homologous and heterologous DNA sequences. Markers were developed for 4 fatty-acyl-acyl carrier protein thioesterase, 2 β-ketoacyl-acyl carrier protein synthase I, 4 β-ketoacyl-acyl carrier protein synthase II, 3 β-ketoacyl-acyl carrier protein synthase III, 3 acyl carrier protein, 2 β-ketoacyl-acyl carrier protein reductase, and 4 enoyl-acyl carrier protein reductase loci. Eighty-eight percent (14 of 16) of the SSCP loci were polymorphic, whereas only 9% (2 of 22) of the AS-PCR loci were polymorphic. These markers were mapped using a Cuphea viscosissima×C. lanceolata F₂ population and produced linkage groups of 10, 3, and 2 loci (3 loci segregated independently). The 10-locus linkage group had every gene but one necessary for the synthesis of 2- to 16-carbon fatty acids from acetyl-CoA and malonyl-ACP (the missing gene family was not mapped). SSCP analysis has broad utility for DNA fingerprinting and mapping genes and gene families. Received: 3 May 1996 / Accepted: 30 August 1996     

Interleukin-21: a modulator of lymphoid proliferation, apoptosis and differentiation

The interleukin-21 (IL-21)-IL-21-receptor system was discovered in 2000. It was immediately of great interest because of the homology of IL-21 to IL-2, IL-4 and IL-15, and of the IL-21-receptor subunit IL-21R to the beta-subunit of the IL-2 receptor, and because the IL-21 receptor also contains the common cytokine-receptor gamma-chain, the protein that is mutated in X-linked severe combined immunodeficiency. As we discuss, IL-21 has pleiotropic actions, from augmenting the proliferation of T cells and driving the differentiation of B cells into memory cells and terminally differentiated plasma cells to augmenting the activity of natural killer cells. Moreover, it has antitumour activity and might have a role in the development of autoimmunity, so these findings have implications for the treatment of cancer and autoimmune diseases.     

Direct 1H n.m.r. determination of the stereochemical course of hydrolyses catalysed by glucanase components of the cellulase complex

The stereochemical courses of the hydrolyses catalysed by three glycosidases have been determined directly by 1H nmr. The anomeric configuration of the initially formed product was ascertained in each case by observation of the chemical shift and coupling constant of the anomeric proton at the new hemiacetal centre. Two of the enzymes investigated, an endo-glucanase and an exo-glucanase are components of the cellulase complex of Cellulomonas fimi. The third enzyme is the beta-glucosidase from almond emulsin. Two of these enzymes, the exo-glucanase and the almond beta-glucosidase catalysed hydrolysis with retention of anomeric configuration, in agreement with previous observations on the almond enzyme. The endo-glucanase catalysed hydrolysis with inversion of configuration, this result being confirmed by optical rotation measurements. This 1H nmr approach has several advantages over other techniques in that it is applicable to a wide variety of glycosidases and substrates and it is non-destructive, allowing recovery of the enzyme.