Mechanism of Ds1 excision from the genome of maize streak virus

Summary We have previously shown that the maize transposable element Ds1 introduced into maize plants by agroinfection can be excised from the genome of geminivirus maize streak virus (MSV). Excision depended strictly on the presence of an active Ac element in the plants. In this study, the excision products or footprints left in the MSV genome after Ds1 excision were extensively characterized and the effects of flanking sequences on Ds1 excision were analysed. Most types of footprints obtained were comparable to those described for Ds1 excision in the maize genome, and could be explained by the models proposed for excision of plant transposable elements. In two revertants, however, some terminal sequences of the Ds1 element were found to have been left behind at the excision site. The finding of this novel type of Ds1 footprint indicated that gene conversion events occurred during and/or after Ds1 excision from the MSV genome. A partial deletion of one copy of the 8 by duplications flanking the Ds1 element had no effect on the frequency or on the types of footprints of Ds1 excision from the MSV genome. Thus, the duplicated 8 by sequences flanking the transposable element are not involved in Ds1 excision. These results, as well as a statistical analysis of the modifications of the bases flanking the Ds1 element after excision, are discussed in terms of excision models.     

Studies on organ weights in naproxen treated rats after intermittent exposure to simulated high altitude

Rats were exposed intermittently for 8h per day over 6 days at simulated high altitude of 20 000 feet. One group of altitude-exposed animals was treated with naproxen, a prostaglandin inhibiting drug. Significant reduction in body weight gain was observed in both altitude-exposed and drug-treated altitude-exposed animals compared to the control group. Right and left ventricular weights and weights of the adrenal glands were increased significantly in altitude-exposed and altitude-exposed drug-treated animals. The weight of the spleen was increased significantly in altitude-exposed animals whereas no such increase of splenic weight was observed in drug-treated altitude-exposed group of animals. On the other hand, the weight of the liver was decreased significantly in both cases. In drug-treated altitude-exposed animals, the unaltered splenic weight was thought to be due to inhibition of the erythropoietic activity.     

Production, purification, and characterization of xylanase from a hyperxylanolytic mutant of Aspergillus ochraceus

Enhancement of the productivity of xylanase and beta-xy-losidase of Aspergillus ochraceus was investigated by multistep mutagenesis. The spores of the wild strain were subjected to UV and N-methyl-N-nitro-N-nitro-soguanidine (NTG). The hyperxylanolytic mutant (NG-13), which showed good clearing on the surface of the xylan-agar plate, secretes xylanase and beta-xylosidase at high levels during growth on commercial xylan and on agricultural wastes. Both liquid and solid state cultures were employed in the study for enzyme production. The xylanase from NG-13 was purified to homogeneity by ammonium sulfate precipitation and gel filtration. This purified enzyme showed a pH optimum of 6.0 and was stable in the range of pH 5 to 10. Prolonged stability of the enzyme was observed at 45 degrees C though its activity was maximal at 50 degrees C. The molecular weight of the enzyme was estimated to be 4.3 x 10(4) by SDS-polyacrylamide gel electrophoresis and 5 x 10(4) by gel filtration on Sephadex G-75. The kinetic data showed that the K(m) and V(max) values for xylan were 1 x 10(-3)M and 19.6 mumol/ min/mg protein, respectively. The enzyme was both more active and thermostable in the presence of K(+)and was inactivated by thiol reagents such as Hg(2+), p-hydroxymercuribenzoate (PHMB), 3', 5'-dithiobis (2'-nitrobenzoic acid) (DTNB), and N-ethylmaleimide (NEM).     

Purification and properties of cyclic AMP-dependent protein kinase from rat epididymis

Two protein kinases (I and II: EC 2.7.1.37) that show a high degree of substrate specificity for protamine rather than histones, phosvitin and casein were partly purified from rat epididymal tissue. The enzymes were present in the cytosol because greater than 80% of the enzymic activity was recovered in the soluble fraction. The kinases required Mg2+ for activity although Co2+ and Mn2+ were partial substitutes. Zn2+ (1 mM) inhibited nearly completely the activity of the enzymes. Both the kinases showed high affinity for activation with cyclic AMP compared to other cyclic nucleotides. Amino acid analysis of 32P-labelled protamine product revealed that the kinases transfer the terminal phosphate of ATP to serine residues of the protein. The isoenzymes I and II showed certain differences in relation to their hydroxyapatite-chromatography profiles, pH activation profiles, heat sensitivity and Km for ATP and cyclic AMP.     

Two forms of phosphoinositol kinase from germinating mung bean seeds

Phosphoinositol kinase, the key enzyme responsible for the biosynthesis of higher inositol phosphates has been isolated from the cotyledons of mung beans germinated for 24 hr and has been resolved into two different forms, phosphoinositol kinase A and phosphoinositol kinase B. Both forms were purified to homogeneity and characterized. The K_m values for ATP with phosphoinositol kinase A (1.78 × 10^?4 M) and phosphoinositol kinase B (3.12 × 10 ^?5 M) showed that phosphoinositol kinase B had a greater affinity for ATP. ATP could be partially replaced as phosphate donor by UTP and phosphoenolpyruvate in the case of phosphoinositol kinase A but not in the case of phosphoinositol kinase B.     

Xanthone and flavonol constituents of Swertia hookeri

The whole plant of Swertia hookeri, collected at flowering has been shown to contain two tri- and nine tetraoxygenated free, glucosyloxy, and stearyl ester xanthones and one flavonol stearyl ester. Among these, three are previously unreported in nature and one was known previously only as a synthetic compound. The xanthones are based on 1,3,5,-, 1,3,5,8- and 1,3,7,8-oxygenated systems with the middle oxygenation pattern predominating. The two ester compounds appeared only at the flowering stage. Plants collected at the pre-flowering stage gave the corresponding free compounds. The biochemical and biological significance of these findings are appraised.     

Induction of N-acetylmannosamine catabolic pathway in yeast.

N-Acetylmannosamine kinase activity is absent from yeast cells grown on N-acetylmannosamine. However, other enzymes of the catabolic pathway, namely, N-acetylmannosamine-2-epimerase, N-acetylglucosamine kinase and glucosamine-6-phosphate deaminase are induced. In addition, a high affinity uptake system (permease) for the uptake of N-acetylglucosamine is synthesized under these conditions. The presence of either N-acetylmannosamine or N-acetylglucosamine as inducer is essential for the induced synthesis of these enzymes. The enzyme synthesis stops and their concentration in the cells declines rapidly as soon as inducer is removed from the medium. N-Acetyl-D-galactosamine can also induce all these enzymes except for N-acetylmannosamine-2-epimerase, suggesting the convergence of catabolic pathways for both the aminosugars at N-acetyl-D-glycosamine. Experiments with inhibitors of macromolecule synthesis suggest that the snythesis of RNA and protein is necessary for the induction of these cyzymes whereas the synthesis of DNA is not.     

RNA synthesis in maturing avian erythrocyte nuclei

The rate of RNA synthesis and its inhibition by α-amanitin in the nuclei of mature and immature avian erythrocytes are increased with the increase in ionic strength of incubation medium. Polyacrylamide gel electrophoresis indicates that heterogeneous species of RNAs are synthesised in the mature and immature erythrocyte nuclei. However, a large number of high molecular weight RNAs are synthesised in the nuclei of immature erythrocytes. Elution profiles on poly(U)-sepharose chromatography indicate that the RNAs synthesised in the nuclei of two types of cell contain poly(A) segments. Sixteen per cent of mature erythrocyte nuclear RNA syntbesised are polyadenylated, while it is 13% in immature erythrocyte nuclei. However, the total RNA synthesised is 2–3 fold higher in immature erythrocyte nuclei than that in mature erythrocyte nuclei.