# Mechanisms of Gonococcal Pilin Antigenic and Phase Variation

> **NIH NIH R37** · NORTHWESTERN UNIVERSITY · 2023 · $521,036

## Abstract

Abstract
 The pathogenic Neisseria are obligate human pathogens that rely on several antigenic variation systems
to colonize and cause disease in the human population. This proposal will further our studies into the molecular
mechanisms for pilin antigenic variation in Neisseria gonorrhoeae. High-frequency gene conversion reactions
mediate extensive changes in the pilin amino acid sequence with segmental recombination between one of 18
silent pilin copies and the single expressed pilin gene. Over the tenure of this grant, we have (1) identified most
of the proteins involved in this process, (2) demonstrated that the pathogenic Neisseria carry diploid
chromosomes that may facilitate gene conversion, (3) shown that the formation of an alternative DNA structure
called a guanine quartet (G4) is necessary for pilin antigenic variation, (4) shown that transcription of a small
RNA within the G4 is necessary for pilin antigenic variation, and (5) that the small RNA forms an RNA-DNA
duplex (an R-loop). We will determine how new pilin variants replace the previous ones during pilin antigenic
variation. We will test the hypothesis that the G4 structure and associated R-loop initiate gene conversion by
altering chromosomal DNA replication. We will define how gene conversion occurs by applying various
approaches to determine the steps between the initiation of the process and the creation of the final variant
pilins by defining the molecules created and the effect of specific mutants on the generation of different
intermediate molecules. Finally, we will test whether the N. gonorrhoeae diploid chromosomes are involved in
gene conversion. The results of these cutting-edge studies will significantly impact the analysis of (1) Neisserial
pathogenesis, (2) mechanisms of antigenic variation in Neisseria and other bacterial gene conversion
mechanisms, and (4) the way programmed recombination is used in many cell types to alter gene expression
or content. These studies will move all these fields forward and continue pilin antigenic variation as a model for
diversity generation systems that use DNA recombination.

## Key facts

- **NIH application ID:** 10753950
- **Project number:** 2R37AI033493-30A1
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Hank S. SEIFERT
- **Activity code:** R37 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $521,036
- **Award type:** 2
- **Project period:** 1994-05-01 → 2028-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10753950

## Citation

> US National Institutes of Health, RePORTER application 10753950, Mechanisms of Gonococcal Pilin Antigenic and Phase Variation (2R37AI033493-30A1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10753950. Licensed CC0.

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