Evolutionary changes in the higher order structure of the ribosomal 5S RNA.

Comparative studies have been undertaken on the higher order structure of ribosomal 5S RNAs from diverse origins. Competitive reassociation studies show that 5S RNA from either a eukaryote or archaebacterium will form a stable ribonucleoprotein complex with the yeast ribosomal 5S RNA binding protein (YL3); in contrast, eubacterial RNAs will not compete in a similar fashion. Partial S1 ribonuclease digestion and ethylnitrosourea reactivity were used to probe the structural differences suggested by the reconstitution experiments. The results indicate a more compact higher order structure in eukaryotic 5S RNAs as compared to eubacteria and suggest that the archaebacterial 5S RNA contains features which are common to either group. The potential significance of these results with respect to a generalized model for the tertiary structure of the ribosomal 5S RNA and to the heterogeneity in the protein components of 5S RNA-protein complexes are discussed.     

Enzymic synthesis,chemical characterisation and Sda activity of GalNAcß1-4[NeuAcα2-3]Galß1-4GlcNAc and GalNAcß1-4[NeuAcα2-3]Galß1-4Glc

The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and¹H-500 MHz NMR spectroscopy. In Sd^a serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity.     

Specific absorption rate in rats exposed to 2,450-MHz microwaves under seven exposure conditions

Both positive and negative biological effects of microwaves on drug actions in rats exposed to 1-mW/cm2, 2,450-MHz microwaves have been reported by several investigators. We conducted dosimetry studies for seven different exposure conditions to determine whether these different results could be due to the rats having been exposed differently. They included anterior and posterior exposures in a circular waveguide, near field, far field with E- or H-field parallel to the long axis of the body and dorsal exposure in a miniature anechoic chamber with E- or H-field parallel to the long axis of the body. The average specific absorption rates (SARs) in the head, tail, and body of the exposed rats were measured by means of a calorimetry system. The local SARs at eight locations in the brain were determined by temperature measurement with Vitek probes. Intensive coupling of energy to the tail when it was exposed parallel to the E-field was shown by thermography. For the same average incident power density, the average SARs in the heads of rats were about two times higher in the circular waveguide than for other exposures. The local SARs in the brain varied for different exposure conditions. Statistical comparisons of SARs under the different exposure conditions are presented.     

Replication of adenovirus mini-chromosomes

We have isolated adenovirus origins of DNA replication from both the right and left ends of the genome, which are functional on linear autonomously replicating mini-chromosomes. The mini-chromosomes contain two cloned inverted adenovirus termini and require non-defective adenovirus as a helper. Replicated molecules are covalently attached to protein, and DNA synthesis is initiated at the correct nucleotide even when the origins are not located at molecular ends. The activity of embedded origins leads to the generation of linear minichromosomes from circular or linear molecules. These observations therefore suggest that sequences within the adenovirus origin of replication position the protein priming event at the adenovirus terminus. Experiments investigating the regeneration of deleted viral inverted terminal repeat sequences show a sequence-independent requirement for inverted sequences in this process. This result strongly suggests that repair results from the formation of a panhandle structure by a displaced single strand. On the basis of these observations we propose a model for the generation of adenovirus mini-chromosomes from larger molecules.     

Ultrastructural and histochemical changes in the murine zona pellucida during the final stages of oocyte maturation prior to ovulation

The ultrastructural morphology of the mouse zona pellucida was studied in preovulatory follicles from the ovaries of immature mice treated with exogenous gonadotrophins. The ovaries were fixed in the presence of cetylpyridinium chloride, which precipitates carbohydrates, so that their loss during fixation and processing is substantially reduced. The semi-thin araldite sections obtained from osmicated material were viewed by conventional light microscopy, while the ultra-thin sections were examined by transmission electron microscopy. A parallel series of semi-thin sections of non-osmicated ovaries was deresined and subsequently stained with periodic acid Schiff (PAS). The morphological appearance of the zona pellucida in preovulatory oocytes changed during the final stages of oocyte maturation. A close correlation was observed between the ultrastructural appearance of the zona pellucida and that observed following PAS staining during the period studied. Real differences were observed in the location, density, and distribution of glycoconjugates within the zona pellucida during the final stages of oocyte maturation prior to and immediately following germinal vesicle breakdown. Similar changes in the zona were observed in adult females autopsied during proestrus and oestrus. The changes in the density and distribution of glycoconjugates are likely to have important consequences for fertilization by affecting sperm-zona binding and sperm-egg interactions.     

Ontogenetic changes in [3H]-spiroperidol binding sites in posthatch chick brain

The ontogenetic development of [3H]-spiroperidol binding sites was measured in the optic tectum, cerebellum, forebrain base, and forebrain roof of 1-, 4-, and 16-day-old chicks. In the chick optic tectum and cerebellum both the density and the total number of [3H]-spiroperidol binding sites increased from 4- to 16-days-posthatch, but no significant differences were found in either brain area across the initial four posthatch days. In the forebrain base, [3H]-spiroperidol receptor density and total binding increased significantly between 1- and 4-days-posthatch, but at 16-days-posthatch there was a slight decrease in receptor density. Binding sites in the forebrain roof were minimal at all ages. As expected, saturation experiments yielded curvilinear plots indicating the presence of high- and low-affinity binding sites. The high-affinity sites probably reflect dopamine D-2 receptors; whereas, the low-affinity sites may reflect other receptor types, possibly serotonin S-2. These results suggest that large doses of haloperidol, which are normally used in chick behavioral research, may produce behavioral effects by antagonizing multiple receptors.     

Effect of pH on exocellular riboflavin production byEremothecium ashbyii

Summary The production of riboflavin byEremothecium ashbyii grown in a chemically defined medium in batch culture was affected by pH of the medium. Highest yields were obtained at constant pH of 4.5 and 5.5, while little or no riboflavin was detected at either pH 3.5 or 8.5. The medium pH also affected cell morphology. When the organism was grown in a stirred tank reactor and an airlift vessel at pH 4.5 very similar levels of riboflavin were obtained.     

Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata

Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice.