A putative replicative form of the abutilon mosaic virus (gemini group) in a chromatin-like structure

Summary The putative replicative form of the abutilon mosaic virus (AbMV), a geminivirus, was purified from infected plants. It was shown to consist of a bipartite genome of 2660 and 2640 bp. This double-stranded DNA has a closed or relaxed circular conformation and part of it is packed in nucleoprotein complexes with a chromatin-like structure. Similarities between the geminiviruses and the animal simian virus 40 are discussed against this back-ground.Cloning was performed under L2/B1 conditions according to the licence of the ZKBS 1526/1This article is based on a doctoral study by A.A. and T.F. in the Faculty of Biology, University of Hamburg     

Growth and development of maxipak wheat as affected by soil salinity and moisture levels

The effect of soil salinity and soil moisture on the growth and yield of maxipak wheat (Triticum aestivum L.) was studied in a lath-house experiment in whih, chloride-sulphate salt mixtures were used to artificially salinize a sandy loam soil from Al-Jadyriah Baghdad. Five soil salinity levels of ECe's equal to 1.7 (Control) 4.2, 5.8, 8.1, 9.4 and 11.0dSm^–1 were prepared and used at 3 levels of available soil moisture depletion, namely, 25, 50, and 75% as determined by weight. Both growth (vegetative) and yield components were studied throughout the growing season.Results showed that increasing the soil salinity from 1.7 to 11.0 dSm^–1, and decreasing the available soil water from 75 to 25% resulted in independent and significant decreases in Mazipak wheat growth and yield components at different stages of plant development. Root growth showed more sensitivity to both available soil water and soil salinity level than other components. It has been concluded that at soil salinity levels of more than 8.0 dSm^–1, available soil water became a limiting factor on wheat growth and the maintenance of 75% of available soil water during the growth period is recommended to obtain satisfactory grain yield.     

Effective lipid lowering diets including lean meat

The plasma lipid and lipoprotein responses to two modified isoenergetic diets including meat were studied in 15 free living men with hyperlipidaemia (mean plasma cholesterol and triglyceride concentrations 8·1 and 3·4 mmol/l). A reference diet (diet A, 42% energy from fat, ratio of polyunsaturated to saturated fatty acids (P:S ratio) 0·2) was compared with a fat reduced diet (diet B, 35% energy from fat, P:S ratio 0·5) and with a further fat modified diet supplemented with fibre (diet C, 27% energy from fat, P:S ratio 1·0). Daily intake of meat and meat products (180 g/day) was the same in each dietary period; that in diet A had a fat content typical of the average British diet, whereas that in diets B and C was based on very lean meat and meat products. During consumption of diet B the plasma cholesterol concentration fell by 8·6% and low density lipoprotein cholesterol by 11%. During consumption of diet C plasma cholesterol fell by 18·5% and low density lipoprotein cholesterol by 23·8%. Triglyceride and high density lipoprotein cholesterol concentrations and body weight did not change appreciably during the study.A modified diet including a moderate amount of lean meat and meat products is compatible with a reduced lipoprotein mediated risk of atherosclerotic heart disease.     

Formation of novel hairpin structures by telomeric C-strand oligonucleotides.

Telomeres are specialized structures at the ends of chromosomes that are required for long term chromosome stability and replication of the chromosomal terminus. Telomeric DNA consists of simple repetitive sequences with one strand G-rich relative to the other, C-rich, strand. Evolutionary conservation of this feature of telomeric repeat sequences suggests that they have specific structural characteristics involved in telomere function. Absorbance thermal denaturation, chemical modification and non-denaturing gel electrophoretic analyses showed that telomeric C-strand oligonucleotides form stable non-Watson-Crick hairpin structures containing C.C+ base pairs. Formation of such hairpins may facilitate previously reported G-strand exclusive interactions.     

Molecular basis of organ-specific selection of viral variants during chronic infection.

Viral variants of different phenotypes are present in the central nervous system (CNS) and lymphoid tissues of carrier mice infected at birth with the Armstrong strain of lymphocytic choriomeningitis virus. The CNS isolates are similar to the parental virus and cause acute infections in adult mice, whereas the lymphoid isolates cause chronic infections associated with suppressed T-cell responses. In this study, we provide a molecular basis for this organ-specific selection and identify a single amino acid change in the viral glycoprotein that correlates with the tissue specific selection and the persistent and immunosuppressive phenotype of the variants. This phenylalanine (F)-to-leucine (L) change at position 260 of the viral glycoprotein was seen in the vast majority (43 of 47) of the lymphoid isolates, and variants with L at this residue were selected in spleens of persistently infected mice. In striking contrast, isolates with the parental sequence (F at residue 260) predominated (48 of 59 isolates) in the CNS of the same carrier mice. Complete nucleotide sequence analysis of the major structural genes of several independently derived (from different mice) spleen isolates showed that these variants were greater than 99.8% identical to the parental virus. In fact, the only common change among these spleen isolates was the F----L mutation at residue 260 of the glycoprotein. These results show that an RNA virus can exhibit minimal genetic drift during chronic infection in its natural host, and yet a single or few mutations can result in the organ-specific selection of variants that are markedly different from the parental virus.     

Body size, age and reproduction in the leopard toad, Bufo pardalis

Data on the relationships between body size and age were obtained for a sample of leopard toads Bufo pardalis from a breeding population of this species from the Cape Peninsula, South Africa. Age was determined by counting the number of lines of arrested growth in histological sections of a digit clipped from each individual. In males there was a positive, but weak, correlation (explaining only 18% of the variance) between body size and age, and in females no correlation at all existed between these two variables. Males which were successful in obtaining matings were not older than unsuccessful males. Age of males at the breeding site ranged from one to three years, whereas females ranged from two to six years old. This represents both the earliest age of reproduction, as well as the greatest difference in longevity between the sexes, documented for an anuran species.     

Site-directed mutagenesis of the alpha subunit of tryptophan synthase from Salmonella typhimurium

Site-specific mutagenesis has been used to prepare two mutant forms of the alpha subunit of tryptophan synthase from Salmonella typhimurium in which either cysteine-81 or cysteine-118 is replaced by a serine residue. These mutant proteins are potentially useful for x-ray crystallographic studies since a heavy metal binding site is specifically eliminated in each mutant. The purified mutant proteins are fully active in four reactions catalyzed by the wild type alpha 2 beta 2 complex of tryptophan synthase. However, the mutant alpha 2 beta 2 complexes dissociate more readily and are less heat-stable than the wild type alpha 2 beta 2 complex. Thus, cysteine-81 and cysteine-118 of the alpha subunit serve structural but not functional roles.     

Potential of the neem tree (Azadirachta indica) for pest control and rural development

The neem tree (Azadirachta indica) contains promising pest-control substances found effective against many economically important pests. These materials are easy to process by village-level industries and easy to use by limited-resource farmers, thereby offering potential for crop protection and off-farm income generation. The tree’s numerous pharmacological and other complementary uses make it doubly attractive for incorporation in large-scale rural development efforts.     

Anti-tubulin immunofluorescence studies of recovery from vinblastine cytotoxicity in Chinese hamster cells

Antitubulin immunofluorescent staining was used to examine the relationship among crystal formation, mitotic arrest, and recovery potential in vinblastine-treated Chinese hamster cells. Although vinblastine caused a mitotic block at concentrations as low as 5 x 10(-9) M, it induced tubulin crystal formation only at concentrations higher than 10(-6) M. At these higher concentrations, cells took 48-72 h to recover after return to normal medium. This extended period of time was apparently needed for breakdown of the crystals and regeneration of normal cytoplasmic microtubules. At concentrations less than 10(-6) M, although the mitotic block was still effective, no crystals were present. Possibly because of this lack of crystal formation, the cells recovered rapidly, generating cytoplasmic microtubules within 30 min, and beginning to undergo mitosis within 60 min. These findings tend to support biochemical evidence that tubulin binds to vinblastine at two types of binding site: a high affinity, low capacity site, responsible for tubulin disaggregation; and a low affinity site, responsible for protofilament splaying.     

Mitotic inhibition and aneuploidy induction by naturally occurring and synthetic estrogens in Chinese hamster cells in vitro

We used a predominantly diploid Chinese hamster cell line to test a number of naturally occurring and synthetic estrogens for their ability to arrest cells at metaphase, their potential for allowing anaphase recovery, and their capability of inducing aneuploid progeny. The chemicals employed included diethylstilbestrol, dienestrol, hexestrol, beta-estradiol, ethynylestradiol and estriol. We also tested progesterone, estrone and testosterone in this regard. Only estrogens and their synthetic analogs caused mitotic arrest and aneuploidy, while progesterone, estrone and testosterone did not cause mitotic disturbances. Among the estrogens, DES was the most effective arrestant on a comparative molar basis, whereas dienestrol was most potent over a wide range of concentrations. Estriol was the least potent as an arrestant but was an effective inducer of aneuploidy. The addition of a metabolic activator (S9) did not alter the ability of DES to arrest mitosis. Following the removal of the drugs, cells were able to quickly reorganize a spindle apparatus and enter anaphase. Diethylstilbestrol, dienestrol, hexestrol, beta-estradiol, ethynylestradiol and estriol caused significant increase in aneuploidy within a narrow range of high concentrations in recovering cell populations. Aneuploidy was induced in a non-random manner. Immunofluorescence studies with anti-tubulin antibody indicate that estrogens may have a mechanism of mitotic arrest similar to that of colchicine and colcemid, viz inhibiting the polymerization of tubulin to form microtubules. These data suggest that the interaction between estrogens and microtubules may mediate the induction of aneuploidy in somatic cells. Aneuploidy induction by DES and similar compounds may be related to their carcinogenic potential.