TraA is the single structural subunit of the pilus found in type IV conjugative transfer systems. This family is generally found in gammaproteobacteria. The pilins show considerable heterogeneity among the different conjugative plasmit types. All of them however contain an N-terminal part which is cleaved off by a leader peptidase (LepB, or similar) to result in a 68-78 amino acid product. Pilins may be further processed by acetylation (in F-like systems by the TraX protein) or by cyclization (in P-like systems by the TraF protein).