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.
Highlights
Neisseria gonorrhoeae is an obligate human pathogen and the causative agent of the sexually transmitted infection gonorrhea
We defined a guanine quartet (G4) structure in the strict human pathogen Neisseria gonorrhoeae that is required for initiating the homologous recombination reactions leading to pilin antigenic variation (Av)
We show a direct link between transcription of a small RNA that initiates within the G4 structure forming sequence and pilin Av and conclude that the process of transcription is necessary for G4 structure formation. sRNAs have emerged as important regulatory molecules in both eukaryotes and prokaryotes, and this is a novel activity of a sRNA in a bacterium
Summary
Neisseria gonorrhoeae is an obligate human pathogen and the causative agent of the sexually transmitted infection gonorrhea. N. gonorrhoeae possesses one pilin expression locus (pilE) and up to 19 silent pilin loci (pilS) residing in up to 6 discrete locations in the genome [12]. Pilin Av occurs as a result of nonreciprocal DNA recombination between any pilS copy and pilE, leading to the expression of a new variant protein [7]. These new variants can be fully functional, poorly expressed or not expressed, and when the pilus is not expressed or poorly expressed there is an obvious change in colony morphology on solid growth medium [13]. The difference between piliated and nonpiliated colony morphologies allows the ability of a strain to undergo pilin (Av) to be assayed [14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
