Assembly of the tail protein of the Bacillus subtilis phage phi 29.

By in vitro complementation we have determined that gene 13 product functions during phi 29 morphogenesis after the formation of 11- particles, specifically in the functional assembly of the tail protein, p9. Protein p9 from 8- but not from 8-13- extracts assembles in vitro into either 11-13- or 12-13- particles. The action of gene 13 product on p9 for its correct assembly has to take place in vivo; no complementation of 12-13- and 9- lysates occurs in vitro. Protein p9, isolated from phi 29-infected cells, copurifies with the 13+ activity and it is present both in 13+ and 13- extracts as an aggregate with dimensions similar to those of the tail assembled in mature phage.