Phase variation of gonococcal pili by frameshift mutation in pilC, a novel gene for pilus assembly

EMBO J. 1991 Feb;10(2):477-88.


Pili prepared from Neisseria gonorrhoeae contain minor amounts of a 110 kd outer membrane protein denoted PilC. The corresponding gene exists in two copies, pilC1 and pilC2, in most strains of N.gonorrhoeae. In the piliated strain MS11(P+), only one of the genes, pilC2, was expressed. Inactivation of pilC2 by a mTnCm insertion resulted in a nonpiliated phenotype, while a mTnCm insertion in pilC1 had no effect on piliation. Expression of pilC was found to be controlled at the translational level by frameshift mutations in a run of G residues positioned in the region encoding the signal peptide. Nonpilated (P-), pilin expressing colony variants that did not express detectable levels of PilC were selected; all P+ backswitchers from these P-, PilC- clones were found to be PilC+. The structural gene for pilin, pilE, was sequenced and found to be identical in one P-, PilC- and P+, PilC+ pair. Most PilC- cells were completely bald whereas the PilC+ backswitcher had 10-40 pili per cell. Thus, a turn ON and turn OFF in the expression of PilC results in gonococcal pili phase variation. These results suggest that PilC is required for pilus assembly and/or translocation across the gonococcal outer membrane.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins / genetics*
  • Bacterial Outer Membrane Proteins / isolation & purification
  • Base Sequence
  • Cloning, Molecular
  • Fimbriae Proteins
  • Fimbriae, Bacterial / physiology*
  • Fimbriae, Bacterial / ultrastructure
  • Frameshift Mutation*
  • Genes, Bacterial*
  • Genetic Variation*
  • Molecular Sequence Data
  • Molecular Weight
  • Mutagenesis, Insertional
  • Neisseria gonorrhoeae / genetics*
  • Neisseria gonorrhoeae / physiology
  • Oligonucleotide Probes
  • Polymerase Chain Reaction
  • Restriction Mapping
  • Sequence Homology, Nucleic Acid


  • Bacterial Outer Membrane Proteins
  • Oligonucleotide Probes
  • Fimbriae Proteins