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Transcription of a cis-acting, noncoding, small RNA is required for pilin antigenic variation in Neisseria gonorrhoeae. | LitMetric

AI Article Synopsis

  • * The study highlights a guanine quartet (G4) structure near the pilE gene that is essential for the gene conversion events leading to pilin variation, and the function of a specific small non-coding RNA (sRNA) related to this process.
  • * Inactivating the sRNA promoter halts pilin antigenic variation, while modifications that strengthen the promoter or replace it allow for normal variation, indicating that the G-rich DNA can only form the G4 structure when the sRNA is being transcribed, initiating recombination events

Article Abstract

The strict human pathogen Neisseria gonorrhoeae can utilize homologous recombination to generate antigenic variability in targets of immune surveillance. To evade the host immune response, N. gonorrhoeae promotes high frequency gene conversion events between many silent pilin copies and the expressed pilin locus (pilE), resulting in the production of variant pilin proteins. Previously, we identified a guanine quartet (G4) structure localized near pilE that is required for the homologous recombination reactions leading to pilin antigenic variation (Av). In this work, we demonstrate that inactivating the promoter of a small non-coding RNA (sRNA) that initiates within the G4 forming sequence blocks pilin Av. The sRNA promoter is conserved in all sequenced gonococcal strains, and mutations in the predicted transcript downstream of the G4 forming sequence do not alter pilin Av. A mutation that produces a stronger promoter or substitution of the pilE G4-associated sRNA promoter with a phage promoter (when the phage polymerase was expressed) produced wild-type levels of pilin Av. Altering the direction and orientation of the pilE G4-associated sRNA disrupted pilin Av. In addition, expression of the sRNA at a distal site on the gonococcal chromosome in the context of a promoter mutant did not support pilin Av. We conclude that the DNA containing the G-rich sequence can only form the G4 structure during transcription of this sRNA, thus providing a unique molecular step for the initiation of programmed recombination events.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3547852PMC
http://dx.doi.org/10.1371/journal.ppat.1003074DOI Listing

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