The Putative Coiled Coil Domain of the φ29 Terminal Protein Is a Major Determinant Involved in Recognition of the Origin of Replication

The linear double-stranded genome of phage φ29 contains a terminal protein (TP) covalently linked at each 5′ DNA end, called parental TP. Initiation of φ29 DNA replication starts with the recognition of the origins of replication, constituted by the parental TP-containing DNA ends, by a heterodimer containing φ29 DNA polymerase and primer TP. It has been argued that origin recognition involves protein-protein interactions between parental and primer TP. Analysis of the TP sequence revealed that the region between amino acids 84 and 118 has a high probability to form an amphipatic α-helix that could be involved in the interaction between parental and primer TP. Therefore, this TP region may be important for origin recognition. To test this hypothesis we introduced various mutations in the predicted amphipatic α-helix and analyzed the functionality of the corresponding purified TP mutants. The results obtained show that the identified putative amphipatic α-helix of TP is an important determinant involved in origin recognition.