title: Propagation of satellite phage P4 as a plasmid.
abstract: Satellite phage P4 has two known options for propagation. In its lytic cycle, its regulatory functions can act in trans to alter the actions of a helper virus (P2), which then provides necessary gene products, including capsid proteins. P4 also can be propagated in the absence of a helper as a prophage, with distinct sites for integration within the Escherichia coli chromosome. We determined that a single spontaneous mutation (vir1) of phage P4 allows a third mode of propagation: as a plasmid (along with continued integration into the host chromosome). Hence, the P4 regulatory element is capable of (i) temperate; (ii) lytic, helper-dependent; and (iii) plasmid modes of development. These findings emphasize the close relationship between defective viruses and plasmids.
mesh_terms: D003001:Cloning, Molecular / Q000379:methods; D003090:Coliphages / Q000235:genetics*; D004261:DNA Replication; D004278:DNA, Superhelical / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics*; D005786:Gene Expression Regulation; D008242:Lysogeny; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D014779:Virus Replication
chemical_list: D004278:DNA, Superhelical