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The bacteriophage P2 ogr gene encodes an essential 72-amino-acid protein which acts as a positive regulator of P2 late transcription. A P2 ogr deletion phage, which depends on the supply of Ogr protein in trans for lytic growth on Escherichia coli C, has previously been constructed. E. coli B and K-12 were found to support the growth of the ogr-defective P2 phage because of the presence of functional ogr genes located in cryptic P2-like prophages in these strains. The cryptic ogr genes were cloned and sequenced. The Escherichia coli rpoA109 mutation, which causes an amino acid substitution in the a subunit of the RNA polymerase, blocks transcription of the P2 late genes (21,56). This block is overcome by suppressor mutations in the P2 ogr gene (56); thus, it appears that Ogr interacts with the RNA polymerase ao subunit in initiation of transcription from the P2 late promoters. Interactions between the ac subunit and other positive regulatory proteins have been implied by the isolation of several rpoA mutations which affect the transcription of different positively regulated E. coli genes (22,25,44,47) and also by recent studies of the E. coli cyclic-AMP receptor protein (34, 35).As a part of our investigations concerning the Ogr protein function and the regulation of its gene, we have previously reported the construction of an ogr-defective mutant phage, P2 dellS, which carries a deletion in the C-terminal half of the ogr gene (9). P2 dellS grows lytically on E. coli C, the standard host for phage P2, only if the Ogr protein is provided in trans from an ogr-expressing plasmid, demonstrating that the ogr gene is essential for P2 lytic growth. In this paper, we report that E. coli B and K-12 strains are able to support growth of P2 dell5 and that this ability is due to the presence of chromosomally located ogr genes carried by cryptic prophages. The presence of an ogr gene in E. coli * Corresponding author. K-12 has recently also been demonstrated by Barreiro andHaggard-Ljungquist (4). When the P2 ogr gene is compared with the cryptic genes, there are few differences in the nucleotide sequences, and most of the differences are silent base substitutions. MATERIALS AND METHODSBacteria, phages, and plasmids. Bacterial strains, phages, and plasmids are listed in Table 1. Strain C-2156 was used as a standard host for P2 dellS (11). The culture media were L broth and L agar (52). Plasmid-containing strains were grown in media containing 100 ,ug of ampicillin per ml (pBluescript SK+ and its derivatives) or 12.5 p,g of tetracycline per ml (pNB56).Burst size determination. Bacteria were grown in L broth at 37°C to an optical density at 600 nm of 0.2, collected by centrifugation at 9,000 x g for 2 min, and resuspended in one-third the original volume of ice-cold L broth containing 5 mM CaCl2. The cells were infected with P2 dellS at a multiplicity of infection of 0.1 and then incubated at 37'C for 8 min for adsorption of the phage. The infected cells were collected by centrifugation at 9,000 x g for 2 min at 4°C and washed ...

The Ogr protein is a 72-residue, zinc-binding transcription factor essential for activation of late gene expression in bacteriophage P2. Analysis of C-terminal truncated proteins generated by stop codon mutagenesis shows that deletion of residues distal to position 51 had negligible effects on Ogr function. More-extensive deletion resulted in unstable products with severely reduced activity. These results, as well as the elfects of other mutations in this region, support the idea that the 21 C-terminal residues are not required for transactivation.The P2 ogr gene encodes a transcription factor essential for activation of the late genes of bacteriophage P2 (for a review, see reference 3). It has been suggested that Ogr binds to promoter regions at a dyad symmetry element centered at position -55 upstream of the operons it controls (10, 25). Furthermore, genetic evidence implies a direct interaction between Ogr and the host RNA polymerase: the rpoA109 allele of the ot subunit of Escherichia coli RNA polymerase specifically imposes a block on P2 late gene transcription which is overcome by suppressor mutations located in the ogr gene (8,24). This suggests that the Ogr protein functions in a transcription initiation complex via specific contacts between Ogr and DNA and also between Ogr and the at subunit of RNA polymerase. Despite considerable efforts, however, no direct experimental evidence for any of the proposed binding interactions of the Ogr protein has yet been obtained, and the mechanism of Ogr action remains elusive.Ogr belongs to a family of functionally and structurally homologous proteins, encoded by P2-and P4-related phages, which show no significant sequence similarity to other known transcription factors. A comparison between Ogr and the related proteins from bacteriophages P4 and 186 and retronphage 4R73 is shown in Figure 1. There is strong conservation of amino acids in the amino-terminal two-thirds of these proteins; seven amino acids, including four cysteines arranged in the pattern CysX2CysX22CysX4Cys, are invariant. This arrangement does not correspond closely to the consensus sequences of any of the known classes of DNA-binding zinc finger proteins (7). While it has been demonstrated that purified Ogr binds zinc (17), the exact role that zinc binding may play in the mode of action of the Ogr protein is still unknown. The carboxy-terminal regions of these proteins show little sequence conservation. They do, however, contain an unusually large number of proline residues and are predicted to be fairly hydrophobic. It has been proposed (16) that this proline-rich region may constitute a transcription activation domain, reminiscent of the proline-rich domain which has been invoked for some eukaryotic transcriptional activators (18).As (14), with reagents, protocols, and bacterial strains supplied in the Phagemid mutagenesis kit (Bio-Rad). Single-stranded, uracil-containing pKG100 template DNA was isolated by infection with the helper phage M13K07 (26). Mutations were identified either by direct se...

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High quality is recommended for drinking water to prevent the transportation of pathogenic bacteria. To ensure its quality, different technologies are applied, and copper-silver ionization is used to maintain the microbiological quality. However, considering that the characteristics of this source vary in different scenarios, it was proposed to evaluate the efficacy of copper-silver ionization for the disinfection of drinking water in Tumbes, Peru. For this evaluation, the physicochemical and microbiological parameters of drinking water were tested at different lengths of copper-silver ionization treatment (10, 20 and 30 minutes). Water samples were collected from 20 houses located in urban areas of Tumbes city where Cu-Ag ionizers (Necon GmbH) were installed. The application of Cu-Ag ionization reduced the microbiological load in the water samples, keeping them below the Peruvian permissible limits (mesophilic bacteria < 500 CFU/100 mL and coliforms < 0 CFU/100 mL). However, in samples with a high microbial load and high electrical conductivity, the microbial load was not completely diminished. Cu-Ag ionization considerably improved the microbiological quality of the water, but some physical parameters, such as pH and electrical conductivity, must be taken into account to further improve the results.