FIG. 6.

Model representation of two different types of pili in Corynebacterium diphtheriae. Shown are two pilus gene clusters in the chromosome of C. diphtheriae (omitted is the third one). Precursor pilin proteins are synthesized in the cytoplasm, transported across the membrane by the Sec machinery, and recognized, polymerized, and anchored by a specific sortase. Sortase SrtA is required for the formation of SpaABC pilus, whereas sortases SrtB and SrtC are specific for the SpaDEF pilus. Pilin proteins are color coded to represent a morphological distinction.