The Multifunctional Bacteriophage P2 Cox Protein Requires Oligomerization for Biological Activity

Abstract

The Cox protein of bacteriophage P2 is a multifunctional protein of 91 amino acids. It is directly involved in the site-specific recombination event leading to excision of P2 DNA out of the host chromosome. In this context, it functions as an architectural protein in the formation of the excisome. Cox is also a transcriptional repressor of the P2 Pc promoter, thereby ensuring lytic growth. Finally it promotes derepression of prophage P4, a nonrelated defective satellite phage, by activating the P4 P LL promoter that controls P4 DNA replication. In this case it binds upstream of the P LL promoter, which normally is activated by the P4 Delta protein. In this work we have analyzed the native form of the Cox protein in vivo, using a bacteriophage cI-based oligomerization assay system, and in vitro, using gel filtration, cross-linking agents, and gel retardation assays. We found that P2 Cox has a strong oligomerization function in vivo as well as in vitro. The in vitro analysis indicates that its native form is a tetramer that can self-associate to octamers. Furthermore we show that oligomerization is necessary for the biological activity by characterizing different cox mutants and that oligomerization is mediated by the C-terminal region.Bacteriophage P2 belongs to a group of serologically related, nonlambdoid phages that can infect several enteric bacterial species (4). It is a temperate DNA phage; i.e., after infection it can either grow lytically, leading to cell lysis and release of progeny phage particles, or form lysogeny. In the latter case, the infected cell survives, and the P2 DNA becomes integrated into the host chromosome through a site-specific recombination event. P2 cox (control of excision) mutants were originally isolated as P2 phages that were unable to liberate phages spontaneously during growth of a lysogenic strain (16). In addition, the cox mutants showed an increased frequency of lysogenization and integrase-mediated site-specific recombination between infecting phages (2, 16).The cox gene is the first gene of the P2 early operon, and it encodes a 91-amino-acid-long, slightly basic polypeptide of 10.3 kDa (12). P2 Cox is a multifunctional protein with at least three distinct functions: (i) P2 prophage excisionase, (ii) transcriptional repressor of P2 Pc promoter, and (iii) transcriptional activator of the unrelated phage P4 P LL promoter.In the site-specific recombination event, P2 Cox protein is directly involved as an architectural protein, where it has been shown to be required for excisive recombination and inhibitory for integrative recombination (32,33). In this case Cox is analogous to Xis. As a transcriptional repressor it represses the P2 Pc promoter that controls the expression of the P2 integrase and the immunity repressor C, thereby ensuring lytic growth (21). At high concentrations it autoregulates its own expression, since it reduces the activity of the early promoter Pe (21). Thus, the P2 Cox protein has in this case a function analogous to that of the well-studied Cro protein.T...

The excision proteins of CTnDOT positively regulate the transfer operon

“…The Cox protein of the phage P2 is also a RDF that activates a promoter and is involved in excision. The Cox protein activates the P LL promoter on the P4 phage by binding upstream, but the mechanism of activation is unknown (Eriksson and Haggård-Ljungquist, 2000). It has two required binding regions; one with a higher affinity for the protein and a lower affinity site located upstream of the -35 region indicating a possible Class I mechanism of activation (Saha, 1989).…”

Bacteriophage Protein–Protein Interactions

“…Cox is multifunctional and acts as a repressor, as well as an excisionase, thereby coupling the transcriptional switch that controls lytic growth versus formation of lysogeny with the integration/excision of the phage genome in or out of the host chromosome. Cox is a tetramer in solution that self-associates to octamers in the absence of DNA (Eriksson and Haggard-Ljungquist, 2000). The transcriptional activator Ogr is required to turn on late gene transcription.…”

Characterization of the Developmental Switch Region of Bacteriophage P2 Hy dis

“…Upon a P4 infection of a P2 lysogenic cell, the P2 prophage becomes derepressed by the P4 E antirepressor (Liu et al, 1997). The surface of the P2 C repressor that interacts with the P4 E antirepressor has been localized by a phage epitope display technique (Liu et al, 1998) and mutational analysis (Renberg- Eriksson et al, 2000). This region is well conserved in the P2 Hy dis C repressor; only 2 of 10 amino acid residues are different and they are conserved with respect to hydrophobicity.…”