SEARCH · Search PubMed

Results for “Coliphages”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources

PubMed1984

Expression of coliphage T7 in aging anucleate minicells of Escherichia coli.

Anucleate minicells produced by a mutated strain of Escherichia coli remain metabolically active for up to 48 h at 37 degrees C. Minicells of increasing age have been infected with the coliphage T7. Infection results in the onset of transcription and translation producing T7 encoded polypeptides. Quantitative and qualitative changes in T7 gene expression result from infection of increasingly old minicells. There is no detectable increase in the frequency of error occurrence in the synthesis of T7 polypeptides in infected old minicells as compared to infected young minicells.

Cell Nucleus↗

PubMed1990

Evidence of neutralizing activity against T3 coliphage in oyster Crassostrea gigas hemolymph.

To investigate defense reactions of bivalve molluscs against viruses, experimental in vitro assays have been developed using T3 coliphage as a test virus. A native neutralizing factor in oyster Crassostrea gigas serum showed high individual variability and was enhanced significantly by repeated sampling of hemolymph from the same oysters. The responsible factor is apparently thermolabile and sensitive to EDTA treatment. Because of an inhibitory effect by the enzymatic inhibitor, phenylmethylsulphonyl fluoride (PMSF), the T3-neutralizing factor may be related to serine protease.

Animals↗

PubMed1982

Sequence changes in coliphage lambda mutants affecting the nutL antitermination site and termination by tL1 and tL2.

The 17-bp sequence designated nutL is required for the N-mediated antitermination of transcription in the major leftward operon of coliphage lambda. The single-stranded sequence can be folded into a hairpin structure. Ten independently isolated spontaneous lambda nutL- mutants have changes that affect the same nucleotide, located in the loop of the hairpin structure, changing the guanine to adenine, thymine or cytosine. Another mutant (lambda nutL3), selected by a different means, has a deletion of one GC base pair and thus eliminates one C in the stem of the hairpin structure, destabilizing it -11.2 to -2.2 kcal/mol. True reversions of the nutL point mutations restore the guanine. The second-site revertant lambda ninL99 was found to have a deletion of 417 bp between the tL1 terminator and the N gene, removing bases +523 to +939 (counted from SL = +1). This deletion include codons for the six carboxy-terminal amino acids of gene N product, but the fusion allows continuation of translation for 53 additional amino acid residues beyond the truncated N gene before reaching a nonsense codon. The fused N product is active.

Bacteriophage lambda↗

PubMed1991

Physical map and genetic early region of the T7-related coliphage, BA14.

The chromosome of the bacterial virus, BA14, a member of the T7 lytic coliphage group, was characterized by direct measurement of its length and construction of a restriction map. The chromosome (39.6 kb) is essentially the same size as T7 (39.9 kb), is devoid of a large number of restriction sites expected for a DNA of this size, and moreover, lacks modification sites for the Escherichia coli Dam and Dcm methyltransferases. The BA14 early region was assigned by testing the ability of specific chromosomal restriction fragments to direct RNA synthesis by E. coli RNA polymerase, and analysis of in vitro RNase III cleavage products of the transcripts. The data support and extend the previous assertion that BA14 is a representative of a distinct T7 subgroup, and limited nucleotide sequence analysis of the BA14 DNA ligase-encoding gene suggests a closer relationship of BA14 to T7 than to T3 phage, another member of the T7 group.

DNA, Viral↗

PubMed1991

Cloning of coliphage-T4 gene pseT and high-level synthesis of polynucleotide kinase in Escherichia coli.

The gene, pseT, of coliphage T4 which encodes polynucleotide kinase (PNK) was cloned directly into an expression plasmid using the polymerase chain reaction. When placed under the control of the trp promoter, the pse T gene can be maintained stably in Escherichia coli and yields high levels of the enzyme upon induction. The system described facilitates purification and provides very high yields of PNK.

Base Sequence↗

PubMed1994

Superinfection exclusion by T-even-type coliphages.

When a bacterial cell is infected with a T-even coliphage, immunity to a superinfecting phage is rapidly established (superinfection exclusion). Two phage-encoded proteins, Imm and Sp, are responsible for this exclusion: Imm blocks DNA transfer across the plasma membrane and partially inhibits release of DNA from the superinfecting virion, and Sp inhibits local degradation of bacterial murein by a phage-associated lysozyme.

Amino Acid Sequence↗

PubMed2003

Activity of coliphage HK022 excisionase (Xis) in the absence of DNA binding.

A mutated excisionase (Xis) protein of coliphage HK022 whose single Cys residue was replaced by Ser does not bind to its two tandem binding sites (X1, X2) on the P arm of attR. Despite its DNA-binding inability the protein showed 30% excision activity of the wild type Xis both in vitro and in vivo. This partial activity is attributed to the interaction of Xis with integrase that is retained in the mutant protein. This protein-protein interaction occurs in the absence of DNA binding.

Bacteriophage HK022↗

PubMed2000

Construction of an efficient expression system for Agrobacterium tumefaciens based on the coliphage T5 promoter.

A versatile expression vector utilizing a promoter of coliphage T5, P(N25) (Gentz and Bujard, 1985. J. Bacteriol. 164, 70-77) and a derivative of the IncW broad-host-range plasmid pJB20 (Beaupré et al., 1997. J. Bacteriol. 179, 78-89) has been developed. This vector successfully expresses virulence proteins of Agrobacterium tumefaciens encoded by virG and a mutant allele of virA, virA (delta1-284, G665D) in Escherichia coli as well as in A. tumefaciens. The signal transduction proteins VirA (delta1-284, G665D) and VirG are fully functional when expressed in Agrobacterium, and the P(N25) driven expression overrides the complex transcriptional regulation present with the native promoters. This expression system will enable a more detailed analysis of the activation events in signal transduction in A. tumefaciens, and we expect it to be useful in other prokaryotes.

Acetophenones↗

PubMed2005

Spectral sensitivity of Bacillus subtilis spores and MS2 coliphage for validation testing of ultraviolet reactors for water disinfection.

The microbicidal UV fluence under polychromatic radiation from UV lamps is typically measured using the DNA absorbance spectrum as a weighting factor for the relative wavelength effectiveness. However, this DNA-based weighting does not necessarily match the spectral sensitivity of the microorganism being tested. Bacillus subtilis spores are often used for UV reactor validation in Europe, while MS2 coliphage is typically used for validation testing in the United States. These organisms were exposed to quasi-monochromatic UV irradiation across the microbicidal spectrum at wavelengths of 214, 230, 240, 254, 265, 280, and 293 nm. MS2 was three times more sensitive to wavelengths near 214 nm compared to the 254 nm output of low-pressure lamps, while B. subtilis spores were most sensitive to wavelengths around 265 nm. Use of these action spectra, compared to the DNA-based weighting, resulted in differences in the calculated polychromatic UV fluence. Consequently, the action spectrum, which is specific for each microorganism, has implications on the uncertainty of UV fluence determination during validation of reactors with polychromatic UV lamps.

Bacillus subtilis↗

PubMed1987

Gene tandem-mediated selection of coliphage lambda-receptive Agrobacterium, Pseudomonas, and Rhizobium strains.

Agrobacterium, Pseudomonas, and Rhizobium spp. have been made receptive to coliphage lambda. To achieve this, recombinant (pTROY) plasmids carrying a constitutive Escherichia coli lamB gene encoding the lambda receptor and expressed from an insertion sequence 3 (IS3) promoter were introduced into various bacteria. Because the wild-type lambda receptor was not expressed in these bacteria, a procedure called the lamB gene tandem protocol was used to select lamB alleles that expressed the lambda receptor. This gene tandem protocol may have general use in adapting genes with nonselectable traits to different organisms. Agrobacterium, Pseudomonas, and Rhizobium strains carrying pTROY41613, which encoded a gene tandem-selected lambda receptor, could be quantitatively transduced with lambda-packaged cosmids. With the ability to confer lambda receptivity on organisms, phage lambda now becomes a general DNA delivery agent.

Journal Article↗

PubMed1998

The Tum protein of coliphage 186 is an antirepressor.

The tum gene of coliphage 186, encoded on a LexA controlled operon, is essential for UV induction of a 186 prophage. Primer extension analysis is used to confirm that Tum is the sole phage function required for prophage induction and that it acts against the maintenance repressor, CI, to relieve repression of the lytic promoters, pR and pB, and thereby bring about lytic development. In vitro experiments with purified proteins demonstrate that Tum prevents CI binding to its operator sites. Tum does not compete with CI for binding sites on DNA, and unlike RecA mediated induction of lambda prophage, the action of Tum on CI is reversible. Mechanisms by which Tum may act against CI are discussed.

Bacterial Proteins↗

PubMed1982

Asymmetric effects of deletions and substitutions on high negative interference in coliphage lambda.

Experiments have been performed to help clarify the role of nonhomologies in phage lambda recombination. Three-factor crosses were carried out, and the frequencies of single and double recombinants in the two adjoining intervals were compared when the central marker was either a double point mutation (v1v3) or deletion (rex-cI deletion) or nonhomologous substitution (imm434). In all cases the lefthand marker was a bio substitution (Fec- phenotype, which does not permit plating on recA-), and the righthand marker was an amber mutation in gene O. Experiments were performed in all four possible arrangements of the central and rightward markers, while selecting for the Fec+ phenotype on the recA- host. As anticipated, high negative interference (HNI) was observed with point mutations, but when the central marker was a substitution nonhomology, HNI was reduced about tenfold. Surprisingly, when the central marker was a simple deletion, a dramatic asymmetry in results was observed, with HNI being exhibited only when the central deletion marker was acquired by the double recombinant. These results indicate that under normal conditions (red+, gam+, rec+) and with noninhibited DNA replication, recombination in coliphage lambda entails a highly asymmetric step that could be at the level of strand transfer or mismatch repair.

Bacteriophage lambda↗

PubMed1995

Involvement of the host initiator function dnaA in the replication of coliphage lambda.

We demonstrate that the initiation of coliphage lambda DNA replication is dependent on the host initiator function dnaA, provided that the lambdoid prophage Rac is absent. Presence of Rac compensated the absence of dnaA function, causing initiation of replication. In dnaAts rac+ cells at 43 degrees, most of parental phage DNA molecules, after one round of theta replication, switched to a replication with features of the sigma mode and produced progeny at high yield. Initiation of replication of the lambda Pts1 mutant at 43 degrees was blocked by dnaA function; however, under dnaA-rac+ conditions all parental phage DNA molecules, after one round of theta replication, switched to the sigma mode and produced progeny at high yield. Taking into account our recent finding that transcriptional activation of ori lambda seems to be dnaA-regulated (to be published elsewhere), we suggest that the DnaA-lambda Pts1 incompatibility occurs at the insertion of the ori lambda-bound lambda O-lambda P-DnaB preprimosome between the complementary lambda DNA strands. The role of Rac and the mechanism of the switch from theta to sigma mode of lambda phage DNA replication are discussed.

Bacterial Proteins↗

PubMed2003

Site-specific recombination links the evolution of P2-like coliphages and pathogenic enterobacteria.

The genome of the tailed temperate coliphage P2 (Myoviridae) contains some genes that probably are horizontally transferred additions to the genome. One of these genes, the Z/fun gene, was recently found intact in the genome of Neisseria meningitidis. We have investigated the presence of P2-like phages, and the genetic variation at the position corresponding to the phage P2 Z/fun locus, in the Escherichia coli reference collection (ECOR). P2-like phages are common in E. coli since they are present in about 30% of the ECOR strains. Hybridizations and PCR amplifications indicate that the overall variation among these phages is small. Amplification of the region corresponding to the phage P2 Z/fun locus in 11 prophages revealed that this is a multivariable locus. Sequencing of the region resulted in 10 completely different sequences but with a similar high AT-content as the Z/fun gene. All sequences contained at least one open reading frame with good transcription and translation signals. All sequences were also surrounded by a highly similar, previously undiscovered, inverted repeat (IR). We also found this IR in genetically unstable regions in pathogenic enterobacteria. This demonstrates that P2-like phages are important factors in the evolution of bacteria, not only because they carry a diversity of lysogenic conversion genes but also because they can act as vectors for single genes. The genes found between the IRs have unknown functions, and only a few clearly similar genes have been found in other bacteria.

Bacteriophage P2↗

PubMed1981

Termination of transcription of the coliphage T7 "early" operon in vitro: slowness of enzyme release, and lack of any role for sigma.

The leftmost portion of the coliphage T7 genome is transcribed by the RNA polymerase Escherichia coli immediately after infection. This "early" operon is delineated by three promoters on the left, and a transcriptional terminator on the right. The terminator is efficient both in vivo, and with highly purified RNA polymerase in vitro. We have studied termination in vitro, using synchronously initiated transcription reactions with low enzyme:DNA ratios. We show that recognition of the stop signal and release of RNA product are relatively rapid. Dissociation of the enzyme from the DNA is quite slow, and probably rate-limiting for re-cycling of the polymerase. It is well established that the sigma subunit of RNA polymerase is required for specific initiation, but redundant during RNA elongation. By exploiting antisigma antiserum we have obtained evidence that sigma is also redundant during all steps of termination in vitro.

Aminoglycosides↗

PubMed1986

Lambdoid coliphages conferring a novel pattern of phage sensitivity on Escherichia coli K12.

Seven temperate coliphages recovered from naturally occurring lysogenic strains of Escherichia coli were found to lyse E. coli C but not K12. Four of these C-specific phages produced mutants (hrk) able to grow on K cells. The K cells harbouring HK253hrk and HK183hrk were converted so that they could adsorb and be lysed by three other non-mutant C-specific phages. HK253, HK183 and two other phages were shown to recombine with phage lambda.

Bacteriophage lambda↗

PubMed2006

Stochastic model of coliphage lambda regulatory network.

The dynamic properties of the regulatory network governing the choice between lytic and lysogenic growths of coliphage lambda is studied using a Markov chain stochastic model. Our computer simulation confirms the finding by Li et al. [Proc. Natl. Acad. Sci. USA 101, 4781 (2004)] on the dynamics of budding yeast: that the biological stationary states are global attractors; the biological pathways of lytic and lysogenic growths are attracting trajectories; and the network functions are robustly designed against structural perturbations. In addition, our model shows the stochastic switch from lysogen to lytic growth, which has been observed in experiments. A definition of pseudoenergy is introduced in the network dynamics to reveal a transitionlike behavior in the system.

Bacteriophage lambda↗

PubMed1994

Inactivation of coliphage Q beta by potassium ferrate.

The kinetics of inactivation of a bacteriophage by potassium ferrate were studied with the F-specific RNA-coliphage Q beta. Inactivation in phosphate buffer (pH 6, 7 and 8) containing ferrate could be described by Hom's model. The inactivation rate depended on the pH. However, the relative effects of ferrate concentration and exposure time on inactivation were not affected by a change in pH from 6 to 8. In a study of the mechanism by which ferrate inactivated the virus, the efficiency of viral inactivation after ferrate decomposed in buffer was assayed. Inactivation was still effective and still followed Hom's equation after the complete decomposition of ferrate ion; however, the efficiency of that inactivation disappeared when sodium thiosulfate was added, suggesting that long-lived oxidative intermediates capable of viral inactivation were generated during the decomposition of ferrate ions.

Allolevivirus↗