New features of 23S ribosomal RNA folding: the long helix 41-42 makes a "U-turn" inside the ribosome

23S rRNA from Escherichia coli was cleaved at single internucleotide bonds using ribonuclease H in the presence of appropriate chimeric oligonucleotides; the individual cleavage sites were between residues 384 and 385, 867 and 868, 1045 and 1046, and 2510 and 2511, with an additional fortuitous cleavage at positions 1117 and 1118. In each case, the 3' terminus of the 5' fragment was ligated to radioactively labeled 4-thiouridine 5'-,3'-biphosphate ("psUp"), and the cleaved 23S rRNA carrying this label was reconstituted into 50S subunits. The 50S subunits were able to associate normally with 30S subunits to form 70S ribosomes. Intra-RNA crosslinks from the 4-thiouridine residues were induced by irradiation at 350 nm, and the crosslink sites within the 23S rRNA were analyzed. The rRNA molecules carrying psUp at positions 867 and 1117 showed crosslinks to nearby positions on the opposite strand of the same double helix where the cleavage was located, and no crosslinking was detected from position 2510. In contrast, the rRNA carrying psUp at position 384 showed crosslinking to nt 420 (and sometimes also to 416 and 425) in the neighboring helix in 23S rRNA, and the rRNA with psUp at position 1045 gave a crosslink to residue 993. The latter crosslink demonstrates that the long helix 41-42 of the 23S rRNA (which carries the region associated with GTPase activity) must double back on itself, forming a "U-turn" in the ribosome. This result is discussed in terms of the topography of the GTPase region in the 50S subunit, and its relation to the locations of the 5S rRNA and the peptidyl transferase center.     

Looking for the LOAEL or NOAEL Concentration of Nickel-Oxide Nanoparticles in a Long-Term Inhalation Exposure of Rats

Rats were exposed to nickel oxide nano-aerosol at a concentration of 2.4 ± 0.4 µg/m³ in a “nose only” inhalation setup for 4 h at a time, 5 times a week, during an overall period of 2 weeks to 6 months. Based on the majority of the effects assessed, this kind of exposure may be considered as close to LOAEL (lowest observed adverse effect level), or even to NOAEL (no observed adverse effect level). At the same time, the experiment revealed genotoxic and allergic effects as early as in the first weeks of exposure, suggesting that these effects may have no threshold at all.     

Electrical resistance of silicon carbide alloyed with nitrogen and articles made from it

Conclusions Nitrogen alloyed silicon carbide has a lower resistivity and is statistically more uniform as regards this factor than ordinary silicon carbide. In batches of articles made in industrial conditions from nitrogen alloyed silicon carbide the electrical resistance is 40% lower, and has half the spread of the values.Translated from Ogneupory, No. 1, pp. 20–21, January, 1988.     

Telematics in undergraduate teaching

The use of telematics in the practice of medicine has received much recent attention but little has been written about the use of these techniques in medical education. This is a report of a pilot study in which an interactive video-conference took place between medical students at the UAE University and their opposite numbers at Aberdeen University. In Aberdeen, the Dean of the Medical Faculty simultaneously taught Aberdeen and UAE students on a clinical case. He was able to confine his activities largely to the correction of misconceptions, the emphasis of important points and the addition of missing information, while the students themselves conducted most of the presentation. The UAE students presented their Community Health projects and had a spirited discussion on them with the Aberdeen students. Recent technological advances have so improved the quality of transmission of both visual and auditory images and at reasonable cost, using the ISDN telephone system, that the feasibility of using this medium as an aid to teaching has suddenly materialized. The experiment showed that the technology was adequate for easy, fully interactive teaching among students from different continents and with different cultural backgrounds. It is particularly suitable for the Arab world where it is the custom to teach males and females separately. The pilot study has pointed out the existence of a medium of communication and teaching which, if proved to be effective, could have far-reaching consequences in the undergraduate and postgraduate teaching of medicine.     

Cytoskeleton-mediated, age-dependent lateral topography of lectin-gold-labelled molecules on the plasma membrane of cultured neurons: a statistical view

In dissociated spinal cord neurons (12-day-old mouse embryo, monolayer culture), an electron microscopic study was carried out to examine quantitatively the rearrangement of wheat-germ agglutinin-gold-labelled molecules on the neuronal somatic surface at two developmental stages (on the fifth and 15th days in vitro), and after cytoskeletal interruptions. In tests, before labelling the cultures were incubated with colchicine or cytochalasin in order to affect microtubules or mostly actin filaments, respectively. Samples of electron micrographs that display soma membrane (profile) fragments were quantified. A set of stochastic geometry approaches was accomplished, which allowed statistical and stereological analysis of labelling. Images that illustrate the lateral (surface) patterns of label were simulated. On the fifth day in vitro, both colchicine and cytochalasin were found to cause an increase in the surface density and aggregation of wheat-germ agglutinin label relative to controls, the effect of cytochalasin being significantly more profound. By the 15th day in vitro, treatment with both drugs led to a similar tendency towards heavy aggregation of wheat-germ agglutinin labels. In contrast, neuron processes showed an opposite tendency of label rearrangement, which suggests lateral migration of labelled molecules, as a result of drug action. Possible molecular mechanisms involved in the phenomena are discussed.     

Methods of Antibiotic Applications as Related to Microbial Quality of Lamb by PCA and Bioluminescence

The effects of different methods of application of chlortetracycline and oxytetracycline on microbial properties of lamb meat were studied. A significant antibacterial effect of antibiotic was found on total mesophilic bacteria count. The mesophilic bacteria level was determined by two methods: the conventional method using Plate Count Agar and bioluminescence. Correlation curves of the CFU and RLU values proved two methods were highly related. Thus for the microbiology quality of meat hygiene the bioluminescence method may be used as a fast and alternative method to PCA. Note that bioluminescence requires a higher degree of skill and attention.