pCD1

pCD1 is a virulence-associated plasmid found in Yersinia species, most notably in Yersinia pestis. It is a circular DNA molecule of roughly 70 kilobases and is an important determinant of pathogenicity in these bacteria. The plasmid carries the genes that encode the type III secretion system (T3SS), a syringe-like molecular apparatus that injects effector proteins into host cells.

The core region of pCD1 includes the ysc gene cluster, which forms the secretion machinery, and the yop gene cluster, which encodes several Yop effector proteins such as YopE, YopH, YopO, YopT, and YopM. These effectors alter host cell signaling and immune responses to promote bacterial survival and replication. Regulation of the pCD1-encoded Ysc/Yop system involves transcriptional regulators such as lcrF, which coordinates expression in response to environmental cues that mimic host conditions.

Role in virulence and biology: The presence of pCD1 is closely linked to the virulence of Yersinia strains. Experimental loss or curing of the plasmid generally results in attenuated virulence, underscoring its essential role in establishing infection. While the exact gene content can vary among strains, the conserved T3SS/Yop machinery is a common feature of the plasmid across pathogenic isolates.

Research significance: pCD1 serves as a widely studied model for type III secretion systems and host–pathogen interactions. It provides a framework for understanding bacterial virulence mechanisms, regulatory networks, and the function of Yops in manipulating host cells. The plasmid’s stability and conservation in pathogenic strains make it a reference point in Yersinia research.

See also: Yersinia pestis, Type III secretion system, Yop proteins, Ysc.