Fractionation of Nitrogen Isotopes during the Uptake and Assimilation of Ammonia by Plants

Two varieties (Nihonbare and Koshihikari) of rice plants (Oryzasativa L.) were grown hydro-ponically with two levels (20 and100 mg N liter ^–1) of ammonia. Variations in levels ofnatural abundance of ¹⁵N (¹⁵N) were analyzed in the ammoniaand organic nitrogen of shoots and roots, as well as in theammonia in the culture solution. There was substantial fractionationof nitrogen isotopes during the uptake of ammonia. When plantsabsorbed a large proportion of ammonia from a solution witha low concentration, less negative ¹⁵N values in plants andhigh positive ¹⁵N values in the ammonia remaining in solutionwere observed. The reverse was found when a smaller fractionof ammonia was absorbed from a solution with a higher concentrationof ammonia. The ^l5N values of ammonia in shoots and roots werehigher than in the respective constituent organic nitrogen,suggesting the fractionation of nitrogen isotopes during theassimilation of ammonia. Wild-type and mutant cells of the cyanobacterium(blue-green alga) Synechococcus PCC 7942 were grown in nitrate-or ammonia-containing medium as the source of nitrogen. Fractionationof nitrogen isotopes during the uptake of nitrate was limited,whereas that during the uptake of ammonia was considerable. ¹ In this report, the term ammonia refers indiscriminately toboth NH₃ or NH₄⁺. (Received June 13, 1991; Accepted September 12, 1991)     

Formation of nodules on non-nodulating soybean T201 after treatment with 2,4-dichlorophenoxyacetate

The formation of effective root nodules on a non-nodulating line (T201) of soybean (Glycine max (L.) Merr.,) was induced by a treatment with 2,4-dichlorophenoxyacetate (2,4-D). The induced nodules, inoculated with mixed Bradyrhizobium japonicum strains A1017 and IRj2101, had a normal internal structure, red in colour and the cells being filled with bacteroids. Externally, the induced nodules were of unusual shape, being paired or gourd-like in form and were attached to thickened roots. The nodules were capable of acetylene reduction (3.1–3.5 moles g^-1 fresh weight nodules h^-1), allowing the growth of plants with dark green leaves.     

Identification of two novel amyloid A protein subsets coexisting in an individual patient of AA-amyloidosis

Amyloid A protein (AA), the major fibril protein in AA-amyloidosis, is an N-terminal cleavage product of the precursor protein, serum amyloid A (SAA). Using mass spectrometry and amino-acid sequencing, we identified and characterized two novel AA protein subsets co-deposited as amyloid fibrils in an patient having AA-amyloidosis associated with rheumatoid arthritis. One of the AA proteins corresponded to positions 2–76 (or 75) of SAA2α and the other corresponded to positions 2–76 (or 75) of known SAA1 subsets, except for position 52 or 57, where SAA1α has valine and alanine and SAA1β has alanine and valine in position 52 and 57, respectively, whereas the AA protein had alanine at the both positions. Our findings (1), demonstrate that not only one but two SAA subsets could be deposited together as an AA-amyloid in a single individual and (2), support the existence of a novel SAA1 allotype, i.e., SAA1^52,57Ala.     

Changes in whole body concentrations of thyroid hormones and cortisol in metamorphosing conger eel

Summary To clarify the hormonal regulation of metamorphosis of the conger eel (Conger myriaster), changes in whole body concentrations of thyroid hormones, thyroxine (T₄) and triiodothyronine (T₃), and cortisol during metamorphosis were examined, as well as the changes in the histological activity of the thyroid gland. In larvae before metamorphosis, T₄ and T₃ levels were less than 5 and 0.15 ng·g^-1 respectively. Levels of T₄ increased to about 30 ng·g^-1 during early metamorphosis, and decreased subsequently. Levels of T₃ increased gradually in early metamorphosis, and then increased abruptly to about 2.0 ng·g^-1 in late metamorphosis. Before metamorphosis, cortisol levels of the leptocephali less than 11 cm in total length were greater than 200 ng·g^-1. Cortisol levels decreased rapidly in larger premetamorphic leptocephali, and low levels were maintained throughout the metamorphic period. Histological observation revealed an activation of the thyroid gland in early metamorphosis; thyroid follicle epithelial cells became columnar and their nuclei larger. Active uptake of colloid by these cells and intensive vascularization of the gland were also observed. By the end of metamorphosis, follicle epithelial cells became squamous, indicating a low level of glandular activity. These results suggest that thyroid hormone plays an important role in regulation of conger eel metamorphosis.Abbreviations AL anal length - TL total length - T ₃ triiodothyronine - T ₄ thyroxine     

Escherichia coli RuvC protein is an endonuclease that resolves the Holliday structure.

Genetic evidence suggests that the Escherichia coli ruvC gene is involved in DNA repair and in the late step of RecE and RecF pathway recombination. To study the biochemical properties of RuvC protein, we overproduced and highly purified the protein. By employing model substrates, we examined the possibility that RuvC protein is an endonuclease that resolves the Holliday structure, an intermediate in genetic recombination in which two double-stranded DNA molecules are linked by single-stranded crossover. RuvC protein cleaves cruciform junctions, which are formed by the extrusion of inverted repeat sequences from a supercoiled plasmid and which are structurally analogous to Holliday junctions, by introducing nicks into strands with the same polarity. The nicked ends are ligated by E.coli or T4 DNA ligases. Analysis of the cleavage sites suggests that DNA topology rather than a particular sequence determines the cleavage site. RuvC protein also cleaves Holliday junctions which are formed between gapped circular and linear duplex DNA by the function of RecA protein. However, it does not cleave a synthetic four-way junction that does not possess homology between arms. The active form of RuvC protein, as studied by gel filtration, is a dimer. This is mechanistically suited for an endonuclease involved in swapping DNA strands at the crossover junctions. From these properties of RuvC protein and the phenotypes of the ruvC mutants, we infer that RuvC protein is an endonuclease that resolves Holliday structures in vivo.     

Alterations in cardiac function and subcellular membrane activities after hypervitaminosis D3

The present study was designed to induce massive accumulation of calcium in the myocardium and to evaluate the effect of calcium overload on myocardial contractile function and biochemical activity of cardiac subcellular membranes. Rats were treated with an oral administration of 500,000 units/kg of vitamin D₃ for 3 consecutive days, and their hearts were sampled on the 5th day for biochemical analysis. On the 4th and 5th days, heart rate, mean aortic pressure, left ventricular systolic pressure and left ventricular dP/dt were significantly lowered in vitamin D₃-treated rats, demonstrating the existence of appreciable myocardial contractile dysfunction. Marked increases in the myocardial calcium (67-fold increase) and mitochondrial calcium contents (24-fold increase) were observed by hypervitaminosis D3. Mitochondrial oxidative phosphorylation and ATPase activity were significantly reduced by this treatment. A decline in sarcolemmal Na⁺, K⁺-ATPase activity was also observed, while relatively minor or insignificant changes in calcium uptake and ATPase activities of sarcoplasmic reticulum were detectable. Electron microscopic examination revealed calcium deposits in the mitochondria after vitamin D₃ treatment. The results suggest that hypervitaminosis D₃ produces massive accumulation of calcium in the myocardium, particularly in the cardiac mitochondrial membrane, which may induce an impairment in the mitochondrial function and eventually may lead to a failure in the cardiac contractile function.     

Properties of the Escherichia coli RuvA and RuvB proteins involved in DNA repair, recombination and mutagenesis

The ruvA and ruvB genes constitute an operon, which is regulated by the SOS system and involved in DNA repair, recombination and mutagenesis. RuvA protein binds to both single-stranded and double-stranded DNA. RuvB protein has weak ATPase activity. RuvA bound to DNA greatly enhances ATPase activity of RuvB. UV-irradiation to supercoiled DNA further enhances the stimulatory effect of RuvA on the RuvB ATPase activity. In the presence of ATP the RuvA-RuvB complex has an activity that renatures cruciform structures formed by heating and gradually cooling supercoiled DNA with an inverted repeat. These findings suggest that the RuvA-RuvB complex interacts with an irregular conformation in damaged DNA and induces conformational changes in DNA using energy provided by ATP hydrolysis, so that it facilitates DNA repair, recombination and error prone replication.     

8-Methyladenosine-substituted analogues of 2-5A: synthesis and their biological activities.

8-Methyladenosine-substituted analogues of 2-5A, p5'A2'p5'A2'p5'(me8A), p5'A2'p5'(me8A)2'p5'(me8A), p5'(me8A)2'p5'(me8A)2'p5'(me8A), and p5'(me8A) 2'p5'A2'p5'A, were prepared via a modification of a lead ion-catalyzed ligation reaction. These 2-5A monophosphates were converted into the corresponding 5'-triphosphates. Substitution of an 8-methyladenosine residue at the third position (2'-terminus) of the oligonucleotides increased the stability to snake venom phosphodiesterase digestion. Both binding and activation of mouse liver 2-5A dependent ribonuclease (RNase L) by the various 8-methyladenosine-substituted 2-5A analogues were examined. Among the 8-methyladenosine-substituted trimer analogues, the analogues with 8-methyladenosine residing in the 2'-terminal position showed the strongest binding affinity and were several times more effective than 2-5A itself as an inhibitor of translation.     

The bialaphos biosynthetic genes ofStreptomyces hygroscopicus: Molecular cloning and characterization of the gene cluster

Summary We have isolated and studied the organization ofStreptomyces hygroscopicus genes responsible for the biosynthesis of the antibiotic herbicide bialaphos. Bialaphos production genes were cloned from genomic DNA using a plasmid vector (pIJ702). Three plasmids were isolated which restored productivity toS. hygroscopicus mutants blocked at different steps of the biosynthetic pathway. Subcloning experiments using other nonproducing mutants showed that four additional bialaphos production genes were also contained on these plasmids. A gene conferring resistance to bialaphos, which was independently cloned using the plasmid vector pIJ61, and an antibiotic-sensitive host (S. lividans), was also linked to the production genes. Cosmids were isolated which defined the location of these genes in a 16 kb cluster.