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  • 1
    Electronic Resource
    Electronic Resource
    The size and position of heterologous insertions in a silent locus differentially affect pilin recombination in Neisseria gonorrhoeae (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Gonococcal pilus antigenic and phase variation result from unidirectional, RecA-dependent recombination of DNA sequences from a silent pilin copy (pilS ) into the expressed pilin gene (pilE ). To develop a quantitative assay for pilin gene recombination that is independent of phase variation, a promoterless cat gene was inserted into pilS, and recombination of ′cat into pilE was detected by selection of chloramphenicol-resistant (CmR) variants expressing ′cat from the pilin promoter. Although RecA-dependent CmR variants occurred, none were generated by the simple transfer of ′cat into pilE. Instead, each CmR variant contained a new pilin locus that was a hybrid of sequences from the pilE and the pilS1::′cat loci in addition to the two starting loci. Therefore, this system could not be used to quantify antigenic variation. However, combined studies of these hybrid loci and of recombination products generated during additional pilS mutational analyses demonstrated that both the size and position of an insertion in pilS differentially affect pilin recombination. Also, the hybrid loci appear to be intermediates of antigenic variation. This enabled the creation of molecular models for the recombination reactions that result in pilin antigenic variation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.00128.x
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  • 2
    Electronic Resource
    Electronic Resource
    Single charge carrier type sensing with a parallel strip pseudo-Frisch-grid CdZnTe semiconductor radiation detector (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 792-794 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improvement in gamma-ray energy resolution is demonstrated for a room-temperature operated CdZnTe semiconductor detector that incorporates a parallel strip pseudo-Frisch-grid detector design. The device construction allows primarily for the measurement of electron charge carriers and not hole charge carriers. The detector is a three-terminal device that requires signal output to only one preamplifier, and its simplistic design offers an alternative method to single charge carrier type sensing to that of coplanar semiconductor gamma-ray detector designs. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120895
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  • 3
    Electronic Resource
    Electronic Resource
    Questions about gonococcal pilus phase- and antigenic variation (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 21 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pathogenic organisms inhabit one of several defined locations within a host where temperature, pH, and nutrients are relatively constant. While the microorganism must adapt to different environments within the host, the host immune system is the most formidable predator that can limit the growth of a pathogen. Neisseria gonorrhoeae (the gonococcus, Gc) is the causative agent of gonorrhoea, and has evolved several systems for varying the antigenicity of different surface antigens, presumably to help evade the effects of the human immune system. The On/Off/On phase variation of surface structure expression also alters the antigenic characteristics of the bacterial cell surface. Antigenic variation of the major subunit of the pilus, pilin, occurs by unidirectional, homologous recombination between a silent locus and the expression locus. The silent loci lie from 1 to 900 kb from the expression locus in the chromosome yet all can donate their sequences to the expression locus. The genetic composition of the pilin loci of two Gc strains has been elucidated, and the types of changes that lead to altered forms of the pilus have been extensively characterized. However, little is known about the precise molecular mechanisms used to allow high-frequency, non-reciprocal, chromosomal recombination between pilin loci or about what regulates the process of maintaining chromosome fidelity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02552.x
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of the pilF—pilD pilus-assembly locus of Neisseria gonorrhoeae (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 16 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Expression of Type IV pili by the bacterial pathogen Neisseria gonorrhoeae appears to be essential for colonization of the human host. Several N. gonorrhoeae gene products have been recently identified which bear homology to proteins involved in pilus assembly and protein export in other bacterial systems. We report here the isolation and characterization of transposon insertion mutants in N. gonorrhoeae whose phenotypes indicate that the N. gonorrhoeae pilF and pilD gene products are required for gonoccocal pilus biogenesis. Mutants lacking the pilD gene product, a pre-pilin peptidase, were unable to process the pre-pilin subunit into pilin and thus were non-piliated. pilF mutants processed pilin but did not assemble the mature subunit. Both classes of mutants released S-pilin, a soluble, truncated form of the pilin subunit previously correlated with defects in pilus assembly. In addition, mutants containing transposon insertions in pilD or in a downstream gene, orfX, exhibited a severely restricted growth phenotype. Deletion analysis of pilD indicated that the poor growth phenotype observed for the pilD transposon mutants was a result of polar effects of the insertions on orfX expression. orfX encodes a predicted polypeptide of 23 kDa which contains a consensus nucleotide-binding domain and has apparent homologues in Pseudomonas aeruginosa, Pseudomonas putida, Thermus thermophilus, and the eukaryote Caenorhabditis elegans. Although expression of orfX and pilD appears to be transcriptionally coupled, mutants containing transposon insertions in orfX expressed pili. Unlike either pilF or pilD mutants, orfX mutants were also competent for DNA transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.tb02420.x
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  • 5
    Electronic Resource
    Electronic Resource
    Differential roles of homologous recombination pathways in Neisseria gonorrhoeae pilin antigenic variation, DNA transformation and DNA repair (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 30 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Neisseria gonorrhoeae (Gc) pili undergo antigenic variation when the amino acid sequence of the pilin protein is changed, aiding in immune avoidance and altering pilus expression. Pilin antigenic variation occurs by RecA-dependent unidirectional transfer of DNA sequences from a silent pilin locus to the expressed pilin gene through high-frequency recombination events that occur at limited regions of homology. We show that the Gc recQ and recO genes are essential for pilin antigenic and phase variation and DNA repair but are not involved in natural DNA transformation. This suggests that a RecF-like pathway of recombination exists in Gc. In addition, mutations in the Gc recB, recC or recD genes revealed that a Gc RecBCD pathway also exists and is involved in DNA transformation and DNA repair but not in pilin antigenic variation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.01089.x
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  • 6
    Electronic Resource
    Electronic Resource
    A peptidoglycan hydrolase similar to bacteriophage endolysins acts as an autolysin in Neisseria gonorrhoeae (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 25 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have identified a gene encoding an autolysin (atlA) from Neisseria gonorrhoeae. The deduced amino acid sequence of AtlA shows significant similarity to the peptidoglycan degrading transglycosylases (endolysins) of bacteriophages lambda and P2, suggesting that the encoded protein also functions in peptidoglycan hydrolysis. An atlA mutant was identical to the wild-type strain in exponential growth rate, but demonstrated reduced lysis and peptidoglycan turnover in the stationary phase of growth. When transferred into a buffer solution, at a pH non-permissive for other gonococcal autolysins, an autolytic activity was detectable in the wild-type strain that was not present in the mutant. The most dramatic phenotype of the mutant occurred after extended time in stationary phase. After approximately 16 h in stationary phase, both strains underwent an apparent replication event, after which the wild-type strain died rapidly whereas the atlA mutant survived considerably longer. Even after both the wild-type and mutant cells were dead, many of the mutant cells maintained intact morphology, whereas the wild-type cells were lysed. These results suggest that AtlA is a peptidoglycan transglycosylase related to bacteriophage endolysins and acts as an autolysin in the stationary phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1997.mmi522.x
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  • 7
    Electronic Resource
    Electronic Resource
    Random shuttle mutagenesis: gonococcal mutants deficient in pilin antigenic variation (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 23 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Shuttle mutagenesis has been adapted to randomly mutate the genome of Neisseria gonorrhoeae (gono-coccus; Gc). A size-restricted plasmid library of Gc strain FA1090 was mutated with the mini-transposon mTnEGNS. Randomness was tested by checking for transposon insertion bias between vector and insert DNA, Gc transformation efficiency of individual mutated clones, and representation of unique clones before and after Gc transformation with a mutated pool of DNA. Mutants created by random shuttle mutagenesis were screened, using a colony-based polymerase chain reaction assay, for the ability to undergo pilin antigenic variation. Out of 8064 mutants screened, 22 unique transposon insertion mutants were found to be antigenic variation deficient (Avd). The Avd mutants were separated into five types according to recombination defect-associated phenotypes, including colony growth, natural DNA transformation competence, and repair of DNA damage caused by ultraviolet radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.2971660.x
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  • 8
    Electronic Resource
    Electronic Resource
    Formation and general characterization of a previously unknown ytterbium silicate (A-type Yb2SiO5) (1997)
    Springer
    Journal of materials science 32 (1997), S. 6135-6139 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract On non-isothermal oxidation of ytterbium nitrogen woehlerite (Yb4Si2O7N2), also known as the J-phase, a previously unknown and possibly metastable modification of Yb2SiO5 was detected. It is isostructural with the A-type RE2SiO5 modifications (RE=rare-earth element). The crystallographic data and stability of this new modification of Yb2SiO5 are discussed and compared with available data on RE2SiO5 compounds. The present results suggest that, in general, oxidation of rare-earth oxynitride phases might prove to be a fruitful method to obtain phases that are metastable or cannot be prepared by standard methods since their low-temperature stability range would require unrealistically long firing periods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018656204229
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  • 9
    Electronic Resource
    Electronic Resource
    Thermochemical and structural investigations (1996)
    Springer
    Journal of thermal analysis and calorimetry 46 (1996), S. 1239-1249 
    Details
    ISSN: 1572-8943
    Keywords: DTA ; galvanic bromine cells for solid electrolytes ; pseudobinary systems ; ABr/SmBr3 ; solution calorimetry ; XRD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The phase diagrams of the systems ABr/SmBr3 were reinvestigated. The findings of Blachnik for the systems withA=Cs, Rb, K were confirmed; however, the dimorphic compound K3SmBr6 is stable only above 572 K. The equilibrium temperature, found bye.m.f.-measurements in a solid state galvanic cell for the reaction KBr+K2SmBr5=L-K3SmBr6, is smaller (522 K). The formation temperature for Rb3SmBr6 is 279 K (DTA) and 256 K (e.m.f.) resp. By solution calorimetry was proved that the compounds Cs2SmBr5 and KSm2Br7 don't exist at 0 K. In the system NaBr/SmBr3 only one hitherto unknown dimorphic compound Na3SmBr3 exists above 473 K. L-Na3SmBr crystallizes in the hexagonal space groupR¯3, above 519 K H-Na3SmBr6 has the monoclinic cryolite-structure. Powder patterns of other compounds not yet investigated — H-/L-A3 SmBr6, ASm2Br7 (A=Cs, Rb, K) and Cs2SmBr5 — were indexed analogously to known structure families. The structure parameters of SmBr3·6H2O were determined by single-crystal measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01979238
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  • 10
    Electronic Resource
    Electronic Resource
    Status of the Transient Gamma-Ray Spectrometer (1995)
    Springer
    Astrophysics and space science 231 (1995), S. 475-478 
    Details
    ISSN: 1572-946X
    Keywords: GRBs ; High Resolution Spectroscopy ; Solid State Detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Transient Gamma-Ray Spectrometer (TGRS) was launched aboard the GGS/WIND spacecraft on November 1, 1994. After several deep space orbits (∼2 yrs) WIND will eventually be injected into a halo orbit around the Sun-EarthL 1 point. TGRS consists of a 215 cm3 high purityn-type Ge crystal which is kept at cryogenic temperatures by a passive radiative cooler. The energy range covered by the instrument is ∼25–8000 keV with an energy resolution of ∼2–3 keV. The primary task of TGRS is to perform high resolution spectroscopy of gamma-ray bursts and solar flares. Additional objectives are the study of transient x-ray pulsars and, using an on-board passive occulter, the long-term monitoring of sources such as the Crab and the Galactic Center. Since launch, TGRS has been performing exceedingly well, and all the important experiment parameters such as background levels, gain, and resolution have proven to be very stable. To date, TGRS has detected 27 GRBs and three solar flares. Preliminary analysis of our data also indicates that TGRS is indeed sensitive to sources such as the Crab and the Galactic Center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00658674
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