B-185. A cis-Acting DNA Element Upstream of the Pilin Expression Locus Is Required for Pilin Antigenic Variation in Neisseria gonorrhoeae

L. A. Cahoon, H. S. Seifert;
Northwestern Univ., Chicago, IL.

Neisseria gonorrohoeae (Gc) is a strict human pathogen that is the causative agent of the sexually transmitted infection, gonorrhea. To help avoid immune surveillance, this organism promotes high frequency gene conversion events between many silent pilin loci and the single expressed pilin locus, pilE; resulting in the production of a variant pilin protein. Two transposon insertions have been isolated in the non-coding region upstream of pilE that block pilin Av (Kline et al 2007, Sechman et al 2005). To define which DNA sequences in the noncoding region upstream of pilE are required for pilin Av, this region was randomly mutagenized using error prone PCR and the mutations were introduced into the Gc chromosome by DNA transformation. 103 transformants unable to undergo pilin Av were selected and DNA sequence analysis revealed that each mutant carried a point mutation in a specific region upstream of pilE. Further characterization of this DNA element by site directed mutagenesis revealed that mutating any one of 12 specific bases in this region blocks pilin Av. We conclude that these 12 bp sequence in the noncoding region upstream of the pilus expression locus defines a cis-acting DNA element required for directing recombination from the silent loci to the expressed pilin gene.