Immunologic studies on hamsters infected with Entamoeba histolytica.

The serologic and cell-mediated immune responses of hamsters exposed to 2 strains of Entamoeba histolytica (HM-1 and HM-19) were evaluated by a series of in vitro tests. The pathogenicity of the 2 strains was evaluated in terms of their ability to produce liver abscesses and spleen enlargement. Antibody response was evaluated by the indirect hemagglutination test. The cellular immune response was assayed by increased DNA synthesis by lymphocytes and migration inhibition of macrophages.     

Glutamic acid decarboxylase activity in striatal slices: Persistent increase following depolarization

When slices prepared from rat corpus striatum were preincubated for 15 min in potassium-enriched Krebs Ringer-Phosphate medium (K⁺-KRP), the activity of glutamic acid decarboxylase measured upon reincubation in normal Krebs-Ringer-Phosphate (KRP) was doubled as compared to GAD activity in slices preincubated in normal KRP. Similarly, when striatal slices were preincubated in KRP containing 100 μM veratridine, GAD activity upon reincubation in normal KRP was increased 66% as compared to activity in slices preincubated in normal KRP. The observed increase in GAD activity was not a function of alterations in glutamate uptake by the slices. These results suggest that GABAergic neurons may regulate transmitter synthesis during the process of depolarization by increasing GAD activity.     

Silver Staining for Nucleolar Organizing Regions of Vertebrate Chromosomes

Refinements to a simple, one-step silver staining technique for nucleolar organizing regions are described. These include fixation of silver stained material with sodium thiosulfate and standardization of silver development conditions for different groups of vertebrates. The central advantages to the method are that it is rapid, reliable, simple, and inexpensive. Additional benefits include (i) consistent and uniform silver staining of nucleolar organizing regions, (ii) few reduced silver deposits elsewhere on the chromosomes or on the slides, (iii) generally unaltered chromosome morphology after silver treatment, and (iv) relative permanence of Permounted preparations. The method works equally well on chromosomes made from cell cultures and from solid tissues of live specimens.     

Mutational analysis of antigen receptor regulation of B lymphocyte growth. Evidence for involvement of the phosphoinositide signaling pathway.

Stimulation of the antigen receptor of WEHI-231 B lymphoma cells with anti-receptor antibodies (anti-IgM) induces irreversible growth arrest. Anti-IgM stimulates two kinds of transmembrane signaling events, phosphorylation of proteins on tyrosyl residues and breakdown of inositol phospholipids, which results in increases of inositol phosphates, diacylglycerol, and calcium. The roles of these reactions in mediating the growth arrest of the B lymphoma cells have not been established. To examine this issue, we took a genetic approach. Mutants of WEHI-231 cells were isolated that were resistant to anti-IgM-induced growth arrest. Five out of seven independent mutants analyzed had normal cell-surface expression of antigen receptors. Although each of these five mutants had tyrosine protein phosphorylation patterns comparable to wild-type cells, they exhibited alterations in the phosphoinositide signaling pathway. Four of the mutants had decreased phosphoinositide breakdown, probably due to an alteration in phospholipase C. Decreased second messenger production may be responsible for the growth-resistant phenotype. Full growth arrest was restored upon addition of the calcium ionophore ionomycin, suggesting that the limiting second messenger was intracellular free calcium. The final mutant appeared to be altered in a component(s) that responds to diacylglycerol and calcium. Taken together, these results provide further evidence that the phosphoinositide pathway is at least partly responsible for mediating antigen receptor regulation of B lymphoma cell growth.     

Expression of Characteristics of Ammonium Nutrition as Affected by pH of the Root Medium

To study the effect of root-zone pH on characteristic responsesof -fed plants, soybeans (Glycine max {L.}Merr. cv. Ransom) were grown in flowing solution culture for21 d on four sources of N (1.0 mol m^–3 , 0.67 mol m^–3 plus 0.33 mol m^–3, 0.33 mol m^–3 plus 0.67 mol m^–3 , and 1.0 mol m^–3) with nutrient solutions maintained at pH 6.0, 5.5, 5.0, and 4.5. Amino acid concentration increased inplants grown with as the sole source of N at all pH levels. Total amino acid concentration in the rootsof -fed plants was 8 to 10 times higher than in -fed plants, with asparagine accounting for more than 70% of the total in the roots of these plants.The concentration of soluble carbohydrates in the leaves of-fed plants was greater than that of -fed plants, but was lower in roots of -fed plants, regardless of pH. Starch concentration was only slightlyaffected by N source or root-zone pH. At all levels of pH tested,organic acid concentration in leaves was much lower when was the sole N source than when all or part of theN was supplied as . Plants grown with mixed plus N sources were generally intermediate between - and -fed plants. Thus, changes in tissue compositioncharacteristic of nutrition when root-zone pH was maintained at 4.5 and growth was reduced, still occurredwhen pH was maintained at 5.0 or above, where growth was notaffected. The changes were slightly greater at pH 4.5 than athigher pH levels. Key words: Ammonium, nitrogen nutrition, root-zone pH, soybean, tissue composition     

Influence of mRNA determinants on translation initiation in Escherichia coli.

We have studied the classic initiation elements of mRNA sequence and structure to better understand their influence on translation initiation rates in Escherichia coli. Changes introduced in the initiation codon, the Shine and Dalgarno sequence, the spacing between those two elements, and in the secondary structures within initiation domains each change the rate of 30 S ternary complex formation. We measured these differences using extension inhibition analysis, a technique we have called "toeprinting". The rate of 30 S initiation complex formation in the absence of initiation factors agrees well with in vivo translation rates in some instances, although in others a regulatory role of initiation factors in 30 S complex formation is likely. Nucleotides 5' to the Shine and Dalgarno domain facilitate ternary complex formation.