Identification and Characterization ofpptA: a Gene Involved in the Phase-Variable Expression ofPhosphorylcholine on Pili ofNeisseriameningitidis

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Abstract
Pili of pathogenicNeisseriaare major virulence factors associated with adhesion, cytotoxicity, twitching motility, autoaggregation, and DNA transformation. Pili are modified posttranslationally by the addition of phosphorylcholine. However, no genes involved in either the biosynthesis or the transfer of phosphorylcholine inNeisseria meningitidishave been identified. In this study, we identified five candidate open reading frames (ORFs) potentially involved in the biosynthesis or transfer of phosphorylcholine to pilin inN. meningitidis. Insertional mutants were constructed for each ORF inN.meningitidisstrain C311#3 to determine their effect on phosphorylcholine expression. The effect of the mutant ORFs on the modification by phosphorylcholine was analyzed by Western analysis with phosphorylcholine-specific monoclonal antibody TEPC-15. Analysis of the mutants showed that ORF NMB0415, now defined aspptA(pilin phosphorylcholine transferase A), is involved in the addition of phosphorylcholine to pilin inN. meningitidis. Additionally, the phase variation (high frequency on-off switching of expression) of phosphorylcholine on pilin is due to changes in a homopolymeric guanosine tract inpptA.