Head-Tail Connector Protein gp15 of Bacteriophage SPP1 and similar proteins
The bacteriophage SPP1 gp15 protein is critical in the assembly of the connector, a specialized structure that serves as an interface for head and tail attachment, as well as a point at which DNA exits the head during infection by the bacteriophage. It forms a dodecameric ring structure that comprises the middle ring of the connector, located between the portal protein (attached to the head) and the gp16 ring (attached to the tail). Binding of the gp15 and gp16 rings to the portal protein is essential to prevent leakage of packaged DNA. gp15 is a component of the mature phage and its mutation results in defective head-tail joining.