Type IV pilin regulation: a transcriptional overview

Type IV pili are filamentous surface structures found in diverse bacterial species that provide specialized functions to bacteria, such as initiating cell aggregation via attachment to host cells. The structural filament is made up of polymers of pilin subunits. Gene expression of major pilins is typically the major factor deciding the timing of Type IV pilus filament assembly. Therefore, the regulation of pilin genes is often independent from other pilus biogenesis genes even when they are located within the same cluster. Such strictly regulated pilin transcription ensures that the pilus filament is expressed only when the bacterial cells require it, such as precise timing for a specialized function, or preventing potentially adverse situations like clearing by host defense systems or cell death by phage infection. This review will focus on the transcriptional regulation of Type IV major pilins found in bacteria, and speculate on the evolution of such regulatory systems by identifying similarities and differences across different bacterial phyla.