Cleavage Site of X174 Gene-A Protein in X and G4 RFI DNA

Abstract

The circular, single-stranded (SS) DNA of bacteriophage ϕX174 is replicated via a double-stranded (DS) replicative form (RF) (Sinsheimer et al. 1962). The replication of ϕX RF DNA has been intensively studied from the viewpoint of clarifying the initiation mechanism of DNA synthesis at the molecular level. ϕX RF DNA replication is under the control of viral gene A, as was first shown by Tessman (1966) for the closely related bacteriophage S13. ϕX RF DNA replication is initiated by the introduction of a single nick in the viral strand of the superhelical, covalently closed, circular, duplex (RFI) DNA which is mediated by the viral gene-A protein (Francke and Ray 1971, 1972). The nick in the viral strand resides at a unique site on the ϕX genome which, surprisingly, is located within viral gene A as shown by in vivo (Baas et al. 1976) and in vitro studies (Ikeda et al. 1976;...