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  • 1
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Recent human H3N2 influenza viruses isolated in Japan and China were characterised from an evolutionary point of view. They appeared to have divided into three minor branch clusters, including 1992–1993, 1993–1994 and 1994–1995 isolates. It was of particular interest to reveal that in addition to amino acid substitutions in the antigenic sites of the HA molecule, amino acid changes occurred at position 226 of the receptor binding site from lysine or glutamine to isoleucine in all strains belonging to the 1994–1995 branch cluster. This is the first evidence of human H3N2 influenza isolates, or any other influenza HA serotypes, to contain a conserved amino acid residue other than lysine or glutamine at this key position.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  Matrix (M) and nonstructural (NS) genes of thirteen equine H3N8 and H7N7 influenza viruses were sequenced and analyzed from an evolutionary point of view. The M and NS genes of H3N8 viruses isolated between 1989 and 1993 evolved into two minor branch clusters, including isolates from Europe and the American continent, respectively. It was noteworthy to reveal that the nucleotide sequences of the M and NS genes of an earlier American strain showed highest homology to those of recent European viruses. “Frozen evolution” was observed in the M and NS genes of A/eq/LaPlata/1/88. It was also evident that the NS gene of an H7N7 virus from 1977 was very similar to that of a 1979-H3N 8 virus, while the M gene was closest phylogenetically to that of the earliest H7N7 virus isolated in 1956. Furthermore, the M2 protein of A/eq/Newmarket/1/77 virus contained a carboxyl terminal deletion of three amino acids. The evolutionary rates of the M and NS genes of H3N8 equine influenza viruses were estimated to be 5.4 × 10−4 and 5.1 × 10−4 substitutions per site per year, respectively, which were slower than those of human viruses.
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  • 3
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  New antigenic variants of B/Yamagata/16/88-like lineage which appeared in the season of 1997 as a minor strain tended to predominate in the following season. Also, we could observe for the first time, three peaks of activity caused by H3N2 virus and two variants of B influenza virus. Antigenic and phylogenetic analyses revealed that B/Victoria/2/87-like variants appeared again in Japan in 1997 after a nine-year absence. Influenza B viruses evolved into three major lineages, including the earliest strain (I), B/Yamagata/16/88-like variants (II), which comprised of three sublineages (II-(i), II-(ii), II-(iii)), and B/Victoria/2/87-like variants (III). Evolution of influenza B virus hemagglutinin was apparently distinguishable from that of influenza A virus, showing a systematic mechanism of nucleotide deletion and insertion. This phenomenon was observed to be closely related to evolutionary pathways of I, II-(i), II-(ii), II-(iii) and III lineages. It was noteworthy to reveal that the nucleotide deletion and insertion mechanism of influenza B virus completed one cycle over a fifty-year period, and that a three nucleotide deletion was again observed in 1997 strains belonging to lineage II-( iii). It was evident that amino acid substitutions accompanying nucleotide insertions were highly conserved.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 398-399 (1999), S. 115-119 
    ISSN: 1573-5117
    Keywords: archeospores ; asexual ; epiphyte ; Porphyra ; reproduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reproductive pattern of Porphyra sp. was observed in laboratory culture. The thalli obtained from both natural populations and from cultures were monostromatic and reniform, obovate to linear-oblanceolate. Under the different culture conditions, no differentiation of sexual cells, spermatia or carpogonia, was observed; propagation occurred by archeospore formation (sensu Magne, 1991), with bipolar germination. Thirty successive generations have been obtained in culture, at temperatures of 12 °C and 15 °C, and each time a laminar gametophytic thallus was produced. It is concluded that Porphyra sp. has a strictly asexual reproductive pattern. This is interpreted as a reproductive adaptation to its epiphytic life form.
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