Structure of bacteriophage SPP1 tail reveals trigger for DNA ejection

Lisboa, Portugal The majority of known bacteriophages have long noncon-tractile tails (Siphoviridae) that serve as a pipeline for genome delivery into the host cytoplasm. The tail extre-mity distal from the phage head is an adsorption device that recognises the bacterial receptor at the host cell sur-face. This interaction generates a signal transmitted to the head that leads to DNA release. We have determined structures of the bacteriophage SPP1 tail before and after DNA ejection. The results reveal extensive structural re-arrangements in the internal wall of the tail tube. We propose that the adsorption device–receptor interaction triggers a conformational switch that is propagated as a domino-like cascade along the 1600 Å-long helical tail structure to reach the head-to-tail connector. This leads to opening of the connector culminating in DNA exit from the head into the host cell through the tail tube