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Transposon Mutagenesis Identifies Sites Upstream of the Neisseria gonorrhoeae pilE Gene That Modulate Pilin Antigenic Variation

Kimberly A. Kline ,^, Alison K. Criss, Anne Wallace, and H. Steven Seifert^*

Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611

Received 19 December 2006/ Accepted 9 February 2007

Gene conversion mediates the variation of virulence-associated surface structures on pathogenic microorganisms, which prevents host humoral immune responses from being effective. One of the best-studied gene conversion systems is antigenic variation (Av) of the pilin subunit of the Neisseria gonorrhoeae type IV pilus. To identify cis-acting DNA sequences that facilitate Av, the 700-bp region upstream of the pilin gene pilE was targeted for transposon mutagenesis. Four classes of transposon-associated mutations were isolated, distinguishable by their pilus-associated phenotypes: (i) insertions that did not alter Av or piliation, (ii) insertions that blocked Av, (iii) insertions that interfered with Av, and (iv) insertions that interfered with pilus expression and Av. Mutagenesis of the pilE promoter did not affect the frequency of Av, directly demonstrating that pilin Av is independent of pilE transcription. Two stretches of sequence upstream of pilE were devoid of transposon insertions, and some deletions in these regions were not recoverable, suggesting that they are essential for gonococcal viability. Insertions that blocked pilin Av were located downstream of the RS1 repeat sequence, and deletion of the region surrounding these insertions completely abrogated pilin Av, confirming that specific sequences 5' to pilE are essential for the recombination events underlying pilin Av.

Published ahead of print on 16 February 2007.

Present address: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110.

Kimberly A. Kline and Alison K. Criss contributed equally to this work.

This article has been cited by other articles:

• Hill, S. A., Woodward, T., Reger, A., Baker, R., Dinse, T. (2007). Role for the RecBCD Recombination Pathway for pilE Gene Variation in Repair-Proficient Neisseria gonorrhoeae. J. Bacteriol. 189: 7983-7990 [Abstract] [Full Text]