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  • Blackwell Science Ltd  (2)
  • 1995-1999  (2)
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  • 1
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 25 (1997), S. 0 
    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
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