A transactivation mutant of satellite phage P4

Abstract

A mutant of satellite phage P4, δ6, was isolated as a thermosensitive mutant on the basis of its plaque-forming ability on Escherichia coli C(P2 +). Complementation tests show that this mutant defines a new P4 gene, called δ. Unlike P4 wild type, P4 δ6 depends on the gene A function of its P2 helper at all temperatures, whether the helper is supplied as a prophage or as a coinfecting phage. The P2 gene A product is required both for P2 DNA replication and for P2 late gene expression (Lindahl, G. (1970) Virology 42, 522–533). P2 DNA replication is critical for growth of P4 δ6, since host mutations which block P2 DNA replication prevent production of P4 δ6 progeny, whereas they allow P4 + to multiply. The δ6 mutation makes P4 unable to activate P2 late mRNA synthesis from nonreplicating P2 phage. Thus, P4 δ6 is defective in transactivation.