Pili of Neisseria gonorrhoeae undergo both phase and structural variation. Phase variation of gonococcal pili can be caused by a RecA-independent on/off switch in PilC, a protein involved in pilus biogenesis. We show here that spontaneous nonpiliated PilC- derivatives as well as PilC-insertional mutants have also acquired sequence alterations in pilE relative to the pilE gene of the piliated MS11mk(P+)-u parent, so that the pilin produced is processed to soluble S-pilin and can be released into the medium. It is proposed that pilin alterations are selected for in PilC-bacteria if the parental nonassembled pilin is toxic to the cells--i.e., is not degradable to S-pilin at rates sufficient to allow viability of the cells. Toxicity is indicated by the extreme instability of certain unassembled pilin sequences and by the low frequency of nonpiliated, pilin+, PilC- variants that emerge from piliated recA-cells. The presence of a point mutation changing leucine-39 to phenylalanine at the cleavage site for S-pilin in one nonpiliated, PilC-, recA-variant relative to its piliated parent is a further argument for a selective mechanism of structural diversity of the gonococcal pilin.
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| rdfs:comment |
Pili of Neisseria gonorrhoeae undergo both phase and structural variation. Phase variation of gonococcal pili can be caused by a RecA-independent on/off switch in PilC, a protein involved in pilus biogenesis. We show here that spontaneous nonpiliated PilC- derivatives as well as PilC-insertional mutants have also acquired sequence alterations in pilE relative to the pilE gene of the piliated MS11mk(P+)-u parent, so that the pilin produced is processed to soluble S-pilin and can be released into the medium. It is proposed that pilin alterations are selected for in PilC-bacteria if the parental nonassembled pilin is toxic to the cells--i.e., is not degradable to S-pilin at rates sufficient to allow viability of the cells. Toxicity is indicated by the extreme instability of certain unassembled pilin sequences and by the low frequency of nonpiliated, pilin+, PilC- variants that emerge from piliated recA-cells. The presence of a point mutation changing leucine-39 to phenylalanine at the cleavage site for S-pilin in one nonpiliated, PilC-, recA-variant relative to its piliated parent is a further argument for a selective mechanism of structural diversity of the gonococcal pilin.
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| uniprot:name |
Proc. Natl. Acad. Sci. U.S.A.
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| uniprot:author |
Jonsson A.B.,
Normark S.,
Pfeifer J.
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| uniprot:date |
1992
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| uniprot:pages |
3204-3208
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| uniprot:title |
Neisseria gonorrhoeae PilC expression provides a selective mechanism for structural diversity of pili.
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| uniprot:volume |
89
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| dc-term:identifier |
doi:10.1073/pnas.89.8.3204
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