Activation of Replication Origins in ϕ29-related Phages Requires the Recognition of Initiation Proteins to Specific Nucleoprotein Complexes

Protein p6 of Bacillus subtilis phage ϕ29 activates the initiation of viral DNA replication by forming a multimeric nucleoprotein complex at the origins of replication, located at both ends of the linear genome. This activation requires a precise positioning of the protein p6 array with respect to the initiation site. To investigate this activation mechanism, we have purified the ϕ29 protein p6 counterparts from the related phages Nf and GA-1 and analyzed the formation of complexes with DNA. In the homologous protein p6-DNA complexes the ϕ29 and Nf protein arrays showed an identical positioning, different than that of the GA-1 protein array. In contrast, in the heterologous complexes the protein showed a different arrangement except in the case of the Nf protein-ϕ29 DNA complex. We have also purified the proteins involved in the initiation of replication (terminal protein and DNA polymerase) from phages Nf and GA-1 and measured the ability of the different p6 proteins to activate homologous and heterologous replication origins. The results obtained indicate that the activation requires not only the formation of a specific nucleoprotein complex but also its specific recognition by the proteins involved in the initiation of DNA replication.This work was supported by Grant 5R01 GM27242-16 from the National Institutes of Health, Grant CHRX-CT92-0010 from the European Economic Community, Grant PB93/0173 from the Dirección General de Investigación Científica y Técnica, and by institutional help from the Fundación Ramón Areces. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.Peer reviewe