Search PubMed⌕ Search

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.

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

At least 1,477 records · Page 82Linked to original sources
PubMed1987

Formation of rolling-circle molecules during phi X174 complementary strand DNA replication.

The primosome is a mobile multiprotein priming apparatus that requires seven Escherichia coli proteins for assembly (the products of the dnaB, dnaC and dnaG genes; replication factor Y (protein n'); and proteins i, n, and n"). While the primosome is analagous to the phage T7 gene 4 protein and phage T4 gene 41/61 proteins in its DNA G-catalyzed priming function, its ability to act similarly also as a DNA helicase has remained equivocal. The role of the primosome in unwinding duplex DNA strands was investigated in the coliphage phi X174 SS(c)----replicative form DNA replication reaction in vitro, which requires the E. coli single-stranded DNA binding protein, the primosomal proteins, and the DNA polymerase III holoenzyme. Multigenome-length, linear, double-stranded DNA molecules were generated in this reaction, presumably via a rolling circle-type mechanism. Synthesis of these products required the presence of a helicase-catalyzed strand-displacement activity to permit multiple cycles of continuous complementary (-) strand synthesis. The participation of the primosome in this helicase activity was supported by demonstrating that other SS(c) DNA templates (G4 and alpha-3), which lack primosome assembly sites, failed to support significant linear multimer production and that replication of phi X174 with the general priming system (the DNA B and DNA G proteins and DNA polymerase III holoenzyme) resulted in a 13-fold lower rate of linear multimer synthesis.

Bacteriophage phi X 174↗
PubMed1977

DNA polymerase III holoenzyme of Escherichia coli. Purification and resolution into subunits.

DNA polymerase III holoenzyme has been purified from Escherichia coli HMS-83, using, as an assay, the conversion of coliphage G4 single-stranded DNA to the duplex replicative form. The holoenzyme consists of at least four different subunits: alpha, beta, gamma, and delta of 140,000, 40,000, 52,000, and 32,000 daltons, respectively. The alpha subunit is DNA polymerase III, the dnaE gene product. The holoenzyme has been resolved by phosphocellulose chromatography into an alpha - gamma - delta complex and a subunit beta (copolymerase III*); neither possesses detectable activity in the G4 system but together reconstitute holoenzyme-like activity. The alpha - gamma - delta complex has been further resolved to yield a gamma - delta complex which reconstitutes alpha - gamma - delta activity when added to DNA polymerase III. The gamma - delta complex contains a product of the dnaZ gene and has been purified from a strain which contains a ColE1-dnaZ hybrid plasmid.

Centrifugation, Density Gradient↗
PubMed1984

Integration of a temperate phage infecting Spiroplasma citri.

A physical map of the genome of a temperate Type 3 spiroplasma-virus, ai, has been constructed. Host DNA has been digested with restriction enzymes, and recombinant DNA clones of ai fragments in coliphage M13 vectors have been used as probes to detect viral DNA sequences integrated into spiroplasmas. All strains of Spiroplasma citri examined contained a deleted form of ai integrated as a cryptic prophage which was unable to confer resistance to ai superinfection. Stable ai lysogens also contained a complete ai genome. We propose that the infecting viral DNA circularizes and integrates adjacent to the cryptic prophage in a site-specific recombination event at unique points in both the virus and host genomes.

Bacteriophages↗
PubMed1984

A programme for the construction of a lambda phage.

Infection of a sensitive host by the lambdoid coliphages can cause death of the bacterial cell by lysis or can lead to a lysogenic cell, with the viral DNA stably integrated into the host chromosome. These alternative responses both require the coordination of several host and phage functions, and lambda infection follows a well controlled developmental plan. The lytic and lysogenic pathways of lambdoid infection are reviewed, with emphasis on the variety of control mechanisms involved in the commitment to a particular pathway.

Bacteriolysis↗
PubMed1980

Studies on phage internal proteins. VI. Interaction of bacteriophage T4 internal proteins with T4 DNA in vivo and in vitro.

Internal proteins are basic proteins bound to the DNA of T4 coliphage. Centrifugation in sucrose gradients was employed to isolate DNA-internal proteins complexes formed in vitro. Polyacrylamide gel electrophoresis of radioactive internal proteins in the presence of sodium dodecyl sulfate followed by autoradiography of the gels was used to identify the DNA-bound proteins and to determine their respective abundance in these complexes as well as in the bacteriophage head. The internal proteins were found to bind to the phage DNA (in vitro experiments) at the same ratio as that of internal proteins associated with the viral DNA within the phage head (in vivo binding).

Centrifugation, Density Gradient↗
PubMed1983

Differential template recognition by the Caulobacter crescentus and the escherichia coli RNA polymerases.

Transcription of Escherichia coli and Caulobacter crescentus phage DNAs by their respective host RNA polymerase was examined to determine their ability to recognize specific transcription signals on the heterologous template. Analysis of coliphage T7 in vitro transcripts showed that, like the E. coli enzyme, the C. crescentus RNA polymerase initiated transcription from the three major T7 early promoters and recognized the terminator at the end of the early region. On the other hand, several differences were found between the C. crescentus and E. coli RNA polymerases with respect to their interaction with Caulobacter phage phiCdl DNA. The rates of open complex formation and RNA elongation were slower when phiCdl DNA was transcribed by the E. coli RNA polymerase. In addition, transcription of phiCdl DNA by the E. coli enzyme produced a subset of transcripts not synthesized by the C. crescentus enzyme. The production of these different transcripts by the E. coli enzyme was dependent on salt concentration and, in at least one case, appeared to be the result of differential termination. Although both enzymes protected the same sites on phiCdl DNA from cleavage with HincII, the E. coli enzyme was unable to form stable complexes with some phiCdl restriction fragments that formed stable complexes with the C. crescentus RNA polymerase. These results indicate that although the C. crescentus RNA polymerase can accurately recognize transcription signals on a heterologous phage template, the E. coli enzyme exhibits altered specificity with a heterologous phage template of higher G + C content.

Bacteriophages↗
PubMed1983

Purification and characterization of an RNA processing enzyme from Caulobacter crescentus.

An RNA processing enzyme has been isolated from Caulobacter crescentus which is specific for double-stranded RNA, has an absolute requirement for monovalent cations, and can be eluted from a poly I:C agarose affinity column in pure form. This enzyme, like RNase III isolated from Escherichia coli, processes precursor ribosomal RNAs and polycistronic phage mRNAs and has a monomeric Mr of approximately 20,000. The two enzymes differ, however, in the recognition of specific cleavage sites and yield different digestion products when either coliphage T7 or C. crescentus phage phi Cdl early mRNA is used as substrate. Two lines of evidence are presented which show that an RNase III activity functions as a processing enzyme in C. crescentus. (a) In an in vitro reaction, C. crescentus phage phi Cdl major early mRNA synthesized in vitro by host RNA polymerase was processed by RNase III to yield RNA species which co-migrated with phage RNA synthesized in vivo in phi Cdl-infected cells, and (b) an in vitro transcript of a C. crescentus DNA clone containing the entire 16 S gene and part of the 23 S gene was processed by C. crescentus RNase III to yield an RNA product which co-migrated with 16 S RNA. The RNase III activity isolated from C. crescentus cell extracts has potential use in the analysis of specific RNA species because it was found to be more stringent in the recognition of cleavage sites than the E. coli enzyme.

Cloning, Molecular↗
PubMedDate not supplied

Investigations on the presence of cyanophages in fresh and sea waters of Romania.

Investigations on the presence of cyanophages in the fresh and sea waters of Romania resulted in the isolation of 31 strains. The host range of the cyanophage isolates showed some particularities as compared with classical cyanophages types. The electron optic study of the cyanophage strains grown in Phormidium sp. revealed the presence of three types of virus particles, differing as regards their tail length, with a morphology similar to that of T-odd coliphages.

Bacteriophages↗
PubMed1981

[Serologic affinity and specificity of action of pseudotuberculosis and coli-dysentery phages].

The study of serological properties, specificity and the range of action has revealed affinity between Y. pseudotuberculosis phages (PST, 3M, Kotlyarova, 2344, 2391), some coliphages (T2, T3, T4) and Sh. dysenteriae phage (dd IV). The existence of serovar III of Y. pseudotuberculosis phages has been established; to this serovar phage PST belongs. Newly isolated 2344 and 2391 belong to serovar I. The problem of the existence of Y. pseudotuberculosis phages as an independent group is discussed.

Bacteriophages↗
PubMed1995

Translational control of maturation-protein synthesis in phage MS2: a role for the kinetics of RNA folding?

The gene for the maturation (A) protein of the single-stranded RNA coliphage MS2 is preceded by an untranslated leader of 130 nt. Secondary structure of the leader was deduced by phylogenetic comparison and by probing with enzymes and chemicals. The RNA folds into a cloverleaf, i.e., three stem-loop structures enclosed by a long-distance interaction (LDI). This LDI is essential for translational control. Its 3'moiety contains the Shine-Dalgarno region of the A-protein gene, whereas its complement is located 80 nt upstream, i.e., about 30 nt from the 5'-terminus of the RNA chain. Mutational analysis shows that this base pairing represses expression of the A-protein gene. We present a model in which translational starts can only take place on nonequilibrated RNA, in which base pairing between the complementary regions has not yet taken place. We suggest that this pairing is kinetically delayed by the intervening sequence, which contains the three hairpins of the cloverleaf. The model is mainly based on the observation that reducing the length of the intervening sequence reduces expression, whereas increasing the length has the opposite effect. In addition, further stabilization of the LDI by a stronger base pair does not lead to a decrease in A-protein synthesis. Such a decrease is predicted to occur if translation would be controlled by the equilibrium structure of the leader RNA. These and other observations fit a kinetic model of translational control by RNA folding.

Base Sequence↗
PubMed1993

DNA determinants of restriction. Bacteriophage T4 endonuclease II-dependent cleavage of plasmid DNA in vivo.

Endonuclease II of coliphage T4 is necessary for the in vivo restriction of plasmid DNA in phage-infected cells. Double-stranded restriction cleavage at 12 sites in pBR322 commenced before 10-min postinfection with T4 at 37 degrees C and proceeded more slowly in the presence of competing phage DNA than in its absence, utilizing the same sites in both cases; in a 200-base pair segment of the plasmid, single-stranded nicks also were frequent. The plasmid sites were cleaved with a speed that varied with the site, yielding frequencies of cleavage at different sites varying between 10 and 90%, at 50-min postinfection. All sites contained good matches to a consensus, 5'-GRCCGCNTYGC-3', most frequently cleaved around the variable central base pair, generating fragments with blunt ends or 1-2-base 5' overhangs. Using the frequency of cleavage to determine a weighted consensus, a larger sequence, 5'-CGRCCGCNTTGSYNGC-3', was identified. Thus, DNA sequence elements 3' to the cut site appear important for rapid cleavage. Several models describing the sequence-dependent structure of DNA suggest structural anomalies around the cleavage sites. The endonuclease II restriction system is most similar to type II systems, although it differs from known type II systems in several respects.

Amino Acid Sequence↗
PubMed1993

[An epidemiological assessment of the results of laboratory research on environmental objects].

On the basis of the experience in antiepidemic protection of troops several methods were worked out to make epidemiological estimation of laboratory researches which were conducted in order to disclose the risk factors that provoke infectious diseases. The main attention was focused on the problem of intestinal infections. It was stressed that the practical evaluation of fecal pollution index of water had to be done taking into account the level of infectious morbidity. In unsatisfactory indices of colimetry a threat of diseases in troops is much higher in the regions with frequent intestinal infections. In unfavourable regions with high viral intestinal infections the studies of water must be done after its purification and decontamination in order to reveal the presence of coliphages. On the basis of catering objects the article gives methods for differential estimation of the results of colon bacillus tests depending on epidemiological signification of environmental objects.

Communicable Disease Control↗
PubMed1993

[Preparation and bacterial expression of a mutant gene for human lymphotoxin].

Using the oligonucleotide directed mutagenesis, a human lymphotoxin (TNF beta) mutant gene lacking 21 N-terminal codons has been obtained. Recombinant plasmid pLT21 for expression of the mutant gene has been constructed. The mutant gene in the plasmid was placed under control of a tandem of constitutive promoters from coliphage T7. A simple procedure for isolation of recombinant protein was developed. The procedure allows to obtain the highly purified biologically active mutant protein with a good yield. During biosynthesis the recombinant protein undergoes a posttranslational processing resulted in the cleavage of N-terminal methionine and leucine residues.

Amino Acid Sequence↗
PubMed1996

Comparative disinfection of secondary-treated sewage with chlorine dioxide and bromine chloride.

A comparison was made of the inactivation rates of Arcobacter butzleri, coliphages, total coliforms, fecal coliforms, fecal streptococci and heterotrophic plate count in secondary sewage effluent using chlorine dioxide (2 and 4 ppm) and bromine chloride (4 or 8 and 12 ppm) as disinfecting agents. Using these doses the ClO2 gave higher reduction percentages (on average more than 99% at 4 ppm) than those obtained with BrCl. The average values of the fecal indicators are well within the legal limits. Arcobacter butzleri was more sensitive to the disinfectants than other bacteria while fecal streptococci were seen to be more resistant. From the chemical point of view no differences were seen between the two disinfectants except that the action of ClO2 was stronger regarding BOD5 than that of BrCl. With the exception of dichloromethane, the concentration of volatile halogenated compounds showed little variation and values were often lower than detection limits.

Bromides↗