In vivo functional relationships among terminal proteins of Bacillus subtilis phi 29-related phages.

Gene 3 of the Bacillus subtilis phage phi 29 encodes the terminal protein (TP), which acts as a primer in the initiation of viral DNA replication. We have developed an in vivo functional assay for the phi 29 TP based on the ability of TP-producing B. subtilis non-suppressor (su-) cells to support DNA replication of a phi 29 sus3 mutant phage. This trans-complementation assay has been used to study in vivo functional relationships between the TP of phi 29 and related phages. Our results demonstrate that phi 29 TP functionally substitutes the TP of phage PZA, whereas replication of phage Nf DNA cannot take place in vivo using the phi 29 TP as a primer.