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 Cox protein of the coliphage P2 is multifunctional; it acts as a transcriptional repressor of the Pc promoter, as a transcriptional activator of the P(LL) promoter of satellite phage P4, and as a directionality factor for site-specific recombination. The Cox proteins constitute a unique group of directionality factors since they couple the developmental switch with the integration or excision of the phage genome. In this work, the DNA binding characteristics of the Cox protein of WPhi, a P2-related phage, are compared with those of P2 Cox. P2 Cox has been shown to recognize a 9 bp sequence, repeated at least 6 times in different targets. In contrast to P2 Cox, WPhi Cox binds with a strong affinity to the early control region that contains an imperfect direct repeat of 12 nucleotides. The removal of one of the repeats has drastic effects on the capacity of WPhi to bind to the Pe-Pc region. Again in contrast to P2 Cox, WPhi Cox has a lower affinity to attP compared to the Pe-Pc region, and a repeat of 9 bp can be found that has 5 bp in common with the repeat in the Pe-Pc region. WPhi Cox, however, is essential for excisive recombination in vitro. WPhi Cox, like P2 Cox, binds cooperatively with integrase to attP. Both Cox proteins induce a strong bend in their DNA targets upon binding.

No abstract

No abstract