A streptomycin-resistant Escherichia coli mutant with ribosomes temperature-sensitive in the suppression of a nonsense codon.

Summary Cell free extracts from a streptomycin-resistant E. coli mutant which is also temperature-sensitive for Q phage were studied for suppression of a nonsense mutation at various temperatures. The streptomycin-resistant ribosomes of the mutant were found to be temperature-sensitive in suppression of an amber mutation in f2 phage coat protein while retaining the ability to synthesize proteins at an elevated temperature (42° C). The restriction of amber suppression at 42° C is assumed to be related to an alteration in the ribosomal protein S12 of the streptomycin-resistant mutant which also causes a change in its electrophoretic mobility.     

Sexual development of patients with isochromosomes for the long arm of the X chromosome

Summary The sexual development of 14 girls with non-mosaic monocentric 46,X,iXq karyotype was studied. Seven out of eight girls were found to have immature secondary sexual characteristics and amenorrhoea, a finding greatly contrasting with that in Triplo-X girls. The relative ineffectiveness of the isochromosome Xq in maintaining fertility may be due to the absence of one short arm, which probably also carries a gonadal determinant. Alternatively, the presence of two inactivation sites on one isochromosome may render the gonadal determinants inactive at an important stage in gonadal development.     

SUCCESSFUL AORTOCORONARY BYPASS SURGERY IN A PATIENT WITH CLASSICAL HEMOPHILIA A

A patient with documented Factor VIII deficiency (classical Hemophilia A) and a history of previous severe intra- and postoperative hemorrhage and transfusion reaction underwent myocardial revascularization for advanced triple vessel coronary artery occlusive disease. The coagulation status was investigated, and a replacement regimen was instituted. The surgical procedure and postoperative course were uneventful.     

Inactivation kinetics and pharmacology distinguish two calcium currents in mouse pancreatic B-cells

Summary Voltage-dependent calcium currents were studied in cultured adult mouse pancreatic B-cells using the whole-cell voltage-clamp technique. When calcium currents were elicited with 10-sec depolarizing command pulses, the time course of inactivation was well fit by the sum of two exponentials. The more rapidlyinactivating component had a time constant of 75±5 msec at 0 mV and displayed both calcium influx- and voltage-dependent inactivation, while the more slowly-inanctivating component had a time constant of 2750±280 msec at 0 mV and inactivated primarily via voltage. The fast component was subject to greater steady-state inactivation at holding potentials between –100 and –40 mV and activated at a lower voltage threshold. This component was also significantly reduced by nimodipine (0.5 m) when a holding potential of –100 mV was used, whereas the slow component was unaffected. In contrast, the slow component was greatly increased by replacing external calcium with barium, while the fast component was unchanged. Cadmium (1–10 m) displayed a voltage-dependent block of calcium currents consistent with a greater effect on the high-threshold, more-slowly inactivating component. Taken together, the data suggest that cultured mouse B-cells, as with other insulin-secreting cells we have studied, possess at least two distinct calcium currents. The physiological significance of two calcium currents having distinct kinetic and steady-state inactivation characteristics for B-cell burst firing and insulin secretion is discussed.     

Purification and characterization of recombinant Pneumocystis carinii thymidylate synthase

Gatalytically active Pneumocystis carinii thymidylate synthase is expressed to the extent of about 4% of the soluble protein in Escherichia coli χ2913 harboring plasmid pUETS-1.8 (U. Edman, J. C. Edman, B. Lundgren, and D. V. Santi, Proc. Natl. Acad. Sci. USA 86, 6503–6507, 1989). Ion-exchange, affinity, hydrophobic, and reactive dye agarose chromatography steps were explored to devise a large-scale purification protocol for P. carinii thymidylate synthase. Sequential DE52, Q-Sepharose, phenyl-Sepharose, and Cibacron Blue F3GA chromatography yielded enzyme that was homogeneous by SDS-PAGE in a yield of over 50%. The sequence of the first 10 amino acid residues of the purified protein was in accord with that predicted from the DNA sequence. Isoelectric focusing gave a pI of 6.2. Kinetic analysis of the purified enzyme revealed that the the K_m values were 4.7 ± 1.3 μM for dUMP and 15.7 ± 4.3 μM for 5,10-methylenetetrahydrofolate, similar to those of many other thymidylate synthases; the κ_cat of the most active preparation was 0.8 s⁻¹. The enzyme is stable for at least 2 months when stored at −80°C in the presence of 40% glycerol, Tris-HCl, and thiol.     

The synovial lining of the rabbit knee: A scanning electron microscopy study of specimens reinforced structurally with tannic acid

Summary Medial and lateral synovial linings of the rabbit knee, structurally reinforced with tannic acid during fixation, were studied in the scanning electron microscope. Low-resolution micrographs revealed, in both linings, gross architecture of four types: accordion-like, lobe-like, fatty areolar, and flattened areas. In high resolution, both cellular and acellular surfaces were recorded. A novel, bubble-like appearance, of unknown nature and origin, accounted for 70% of both linings. No definite correlation between anatomical location, gross type, or microarchitectural pattern was noted.     

A repetitive DNA element,associated with telomeric sequences in Drosophila melanogaster,contains open reading frames

He-T sequences are a complex repetitive family of DNA sequences in Drosophila that are associated with telomeric regions, pericentromeric heterochromatin, and the Y chromosome. A component of the He-T family containing open reading frames (ORFs) is described. These ORF-containing elements within the He-T family are designated T-elements, since hybridization in situ with the polytene salivary gland chromosomes results in detectable signal exclusively at the chromosome tips. One T-element that has been sequenced includes ORFs of 1,428 and 1,614 bp. The ORFs are overlapping but one nucleotide out of frame with respect to each other. The longer ORF contains cysteine-histidine motifs strongly resembling nucleic acid binding domains of gag-like proteins, and the overall organization of the T-element ORFs is reminiscent of LINE elements. The T-elements are transcribed and appear to be conserved in Drosophila species related to D. melanogaster. The results suggest that T-elements may play a role in the structure and/or function of telomeres.by W. Hennig     

Experimental and clinical studies of neonatal eeg mapping--methodical prerequisites and data interpretation.

To investigate whether the sampling theorem was fulfilled up to now in experimental and clinical EEG-mapping of neonates and to determine the "smearing effect" of EEG transmission by the leading media up to the skin, EEG-maps from 5 slightly anaesthetized term newborn piglets and 8 healthy human newborns were calculated. A spatial sampling rate of 1-2 cycles per cm is necessary for a sufficient reproduction of surface EEG topology in newborn piglets showing activity maxima within motor projection zones. In human neonates, 8-channel mapping gave insufficient results, whereas state and EEG pattern related 16-channel maps provided sufficiently constant, but not complete pattern. Simultaneous maps from epidural and epiossal, and epiossal, and surface recordings in newborn piglets showed only small "smearing" effects. We conclude, the more topical interpretation chances exist, like in neonates with smaller "smearing" effects of transmission media, the more complete uptake of original data for mapping is necessary. Up to now, it is done seldomly.     

The small-scale production of [U-C]acetylene from BaCO3: Application to labeling of ammonia monooxygenase in autotrophic nitrifying bacteria

A small-scale method has been adapted from an established procedure for the generation of [U-¹⁴C]acetylene from inexpensive and commonly available precursors. The method involves the fusing of Ba¹⁴CO₃ with excess barium metal to produce Ba¹⁴C₂. The BaC₂ is reacted with water to generate acetylene which is then selectively dissolved into dimethyl sulfoxide (DMSO). The results presented demonstrate the effect of Ba:BaCO₃ ratio on the concentrations of various gases released during the hydrolysis reaction and quantify the selectivity of the DMSO-trapping process for each gas. [U-¹⁴C]-Acetylene generated by this method has been used to inactivate ammonia monooxygenase in three species of autotrophic nitrifying bacteria: Nitrosomonas europaea, Nitrosococcus oceanus, and Nitrosolobus multiformis. Our results demonstrate that acetylene inactivation of this enzyme in all three species results in the covalent incorporation of radioactive label into a polypeptide of apparent M_r of 25,000–27,000, as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography.