Termination and reinitiation signals of bacteriophage phi X174 rolling circle DNA replication

The nucleotide sequence requirements for termination and reinitiation of rolling circle DNA replication within the 30-bp phi X174 origin region were studied. Plasmids were constructed which contained a complete and a partial phi X174 origin region in the same orientation. The partial origin consisted of the first 16, 24, 25, 26, 27, or 28 bp of the origin region. Plasmids harboring a complete origin region are subject to rolling circle DNA replication and packaging of single-stranded plasmid DNA into phage coats in phi X174 or G4 phage infected cells. The plasmids with a complete and partial origin region were tested in these in vivo transduction systems. The results lead to the following conclusions: The phi X174 and G4 in vivo transduction systems are useful in studying termination and reinitiation of rolling circle DNA replication. The first 24 bp of the origin region are sufficient for termination of a round of rolling circle DNA replication coupled to DNA packaging. The first 16 bp, however, are not recognized as a termination signal. Reinitiation of rolling circle DNA replication coupled to DNA packaging on a partial origin region occurs with low frequency.