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At least 721 records · Page 40Linked to original sources
PubMed1996

Induction of lambda prophage by 213 nm laser radiation: a quantitative comparison with 193 nm excimer radiation using image analysis.

We compared the DNA damage produced by radiation from two UV laser wavelengths, 213 nm and 193 nm, with that produced by noncoherent 254 nm radiation. Following irradiation of Escherichia coli BR339, a bacteriophage lambda lysogen containing the lacZ gene, pro-phage induction was measured by assaying for beta-galactosidase. Because of the limited penetration by UV laser wavelengths an agar overlay of the lysogen was used as the irradiation target. Irradiation of 254 nm was performed in buffer suspension followed by transfer of 5 microL spots onto assay plants. Computer image analysis was used to monitor the rate of product formation, observed as an increase in optical density of the irradiated zones on assay plates. We found that the rate of product formation was a more reproducible unit of comparison than the optical density present at the end of the reaction. Although the rate of product formation was not linearly related to enzyme concentration, the data could be fit to a simple logarithmic function. Using this method, we concluded that the DNA damaging ability of 213 nm radiation was 10 times more efficient than 193 nm radiation and about 100 times less efficient than 254 nm noncoherent radiation.

Bacteriophage lambda↗
PubMed1973

Induction of prophage in Streptococcus lactis C2 by ultraviolet irradiation.

Streptococcus lactis C2 has been used extensively by many laboratories in studies on the metabolism of lactic streptococci. By using ultraviolet irradiation as the inducing agent, this organism was shown to release a small bacteriophage, indicating that it is a lysogenic strain. The induced phage had a head approximately 40 nm in diameter and a tail length and width of about 180 and 6 nm, respectively. A structure resembling a collar was observed. Attempts to isolate a sensitive indicator strain for the virus were unsuccessful.

Bacteriophages↗
PubMed1997

Promoter activities in Vibrio cholerae ctx phi prophage.

Comparison of cholera toxin (CT) production directed by different gene constructs and S1 nuclease mapping revealed the presence of a ctxB-specific promoter within the ctxA coding sequence. Initiation of transcription in this region occurred in wild-type El Tor and classical biotype choleragenic vibrios. We propose that transcription from the ctxB-specific promoter and a stronger ribosomal binding site on the ctxB mRNA synergistically contribute to achieve the correct (5B:1A) subunit stoichiometry. Plasmid pB, a CT promoterless vector expressing only CTB, was used to detect promoter activity by restoration of A-subunit synthesis. Promoter activity expressed in vitro and in vivo was detected upstream of the zonula occludens toxin gene, suggesting that this factor could be produced in vivo to contribute to fluid accumulation. No promoter activity was detected in vitro and in vivo upstream from the accessory cholera enterotoxin gene.

Base Sequence↗
PubMed1976

Repair deficiency, mutator activity, and thermal prophage inducibility in dna-8132 strains of Bacillus subtilis.

A ts mutation, dna-8132 (Hara and Yoshikawa, 1973), in the region of chromosome replication origin of Bacillus subtilis was found to cause pleiotropic effects at a permissive temperature (30 C). Strains carrying this mutation were lethan at 48 C but exhibited higher spontaneous mutation frequency and a lower capacity for repairing radiation damages at 30C. Introduction of the polA59 (Gass et al., 1971) mutation further enhanced the repair deficiency and the mutator activity. These results suggest that the dna-8132 gene product may be directly involved in chromosome replication and repair. SPO2 lysogens carrying this mutation produced mature phages upon a temperature shift from 30 to 48 C. Phage production at nonpermissive temperature suggests that there are few defects in the precursors of deoxyribonucleic acid synthesis in the mutant.

4-Nitroquinoline-1-oxide↗
PubMed1983

Evidence for positive regulation of plasmid prophage P1 replication: integrative suppression by copy mutants.

Like low-copy-number plasmids including P1 wild type, multicopy P1 mutants (P1 cop, maintained at five to eight copies per chromosome) can suppress the thermosensitive phenotype of an Escherichia coli dnaA host by forming a cointegrate. At 40 degrees C in a dnaA host suppressed by P1 cop, the only copy of P1 is the one in the host chromosome. Trivial explanations of the lack of extrachromosomal copies of P1 cop have been eliminated: (i) during integrative suppression, the P1 cop plasmid does not revert to cop+; (ii) the dnaA+ function of the host is not required to maintain P1 cop at a high copy number; and (iii) integrative recombination does not occur within the region of the plasmid involved in regulation of copy number. Since there are no more copies of the chromosomal origin (now located within the integrated P1 plasmid) than in a P1 cop+-suppressed strain, the extra initiation potential of the P1 cop is not used to provide multiple initiations of the chromosome. When a P1 cop-suppressed dnaA strain was grown at 30 degrees C so that replication could initiate from the chromosomal origin as well as from the P1 origin, multicopy supercoiled P1 DNA was found in the cells. This plasmid DNA was lost again when the temperature was shifted back to 40 degrees C.

Chromosomes, Bacterial↗
PubMed1985

Genetic analysis of spo0A and spo0C mutants of Bacillus subtilis with a phi 105 prophage merodiploid system.

An 8.0-kilobase chromosomal fragment of Bacillus subtilis which contained an intact spo0A gene was recloned onto temperate phage phi 105 from the rho 11dspo0A+-1 transducing phage. A specialized transducing phage, phi 105-dspo0A+-1, was constructed and used to transduce the spo0A12 mutant strain 1S9. A Spo+ transductant which was a single lysogen of the phi 105dspo0A+-1 transducing phage was isolated. From competent cells of this Spo+ transductant was isolated a Spo- (Spo0A) strain which was immune to phi 105. It was used to prepare a lysate of the phi 105dspo0A12 phage. Transduction of the spo0C9V recE4 strain with the phi 105dspo0A12 and phi 105dspo0A+-1 phages was carried out. The phi 105dspo0A+-1 phage gave rise to a large number of heat-resistant cells, but the phi 105dspo0A12 phage formed no heat-resistant cells. These results indicate that the spo0A12 and spo0C9V mutant genes do not complement each other in the ability to sporulate and that the spo0C9V mutation is located within the spo0A gene. Although the spo0C9V strain was completely asporogenous, the spo0C9V/spo0C9V diploid strain produced heat-resistant cells at a frequency of ca. 10(-3) in the sporulation medium. This result indicates that two copies of the spo0C9V mutant gene partially restore the ability of these cells to sporulate.

Alleles↗
PubMed1992

Rapid mapping in Salmonella typhimurium with Mud-P22 prophages.

A new method for mapping mutations in the Salmonella typhimurium chromosome is described and applied to the localization of novel regulatory mutations affecting expression of the nirB (nitrite reductase) gene. The mapping technique is also illustrated by the mapping of mutations in genes affecting carbohydrate catabolism and biosynthetic pathways. The new mapping method involves use of the hybrid phage MudP and MudQ (together referred to as Mud-P22), originally constructed by Youderian et al. (Genetics 118:581-592, 1988). This report describes a set of Mud-P22 lysogens, each member of the set containing a different Mud-P22 insertion. The insertions are scattered along the entire Salmonella genome. These lysogens, when induced by mitomycin C, generate transducing lysates that are enriched (45- to 1,400-fold over the background, generalized transducing particle population) for transducing particles containing bacterial DNA that flanks one side of the insertion. We demonstrate that within the set of lysogens there can be found at least one Mud-P22 insertion that enriches for any particular region of the Salmonella chromosome and that, therefore, all regions of the chromosome are discretely enriched and represented by the collection as a whole. We describe a technique that allows the rapid and facile determination of which lysate contains enriched sequences for the repair of a mutant locus, thereby allowing the determination of the map position of the locus. This technique is applicable to those mutations for which the wild-type allele is selectable. We also describe a procedure whereby any Tn10 insertion can be mapped by selecting for the loss of Tetr.

Bacteriophages↗