Abstract
A new model for the adsorption of bacteriophage P22 to its host Salmonella typhimurium is proposed. The main feature of this model is that only three of the six tail proteins found on the mature phage function during adsorption. This model explains why there is a difference in the specific endoglycosidase activity of the tail protein of mature virions as opposed to unattached tail protein. It also accounts for the cubic relationship between p.f.u. and tail protein concentration in in vitro assembly experiments.