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E Ljungquist

Publications and source records attributed to E Ljungquist.

17 recordsLinked to original sources
PubMed1984

DNA sequences of the repressor gene and operator region of bacteriophage P2.

The nucleotide sequence of the repressor gene C of the temperate phage P2 has been determined. It codes for a nonbasic polypeptide, 99 amino acids long. Twelve repressor-defective mutants have been mapped. All but one are located within the presumed coding part of the gene. There is a strong promoter sequence and an 8-base-pair inverted repeat preceding the gene. The P2 repressor protein shows structural similarity to other DNA-binding proteins. The operator region for the early replication functions was located by sequencing the DNA of three virulent mutants. The sequence indicates that there are two repressor-binding sites. In addition, one of the sites shows sequence homology with part of the operator region of the biotin operon of Escherichia coli.

Amino Acid Sequence↗
PubMed1983

Properties and products of the cloned int gene of bacteriophage P2.

Fragments of DNA of the temperate phage P2, generated by treatment with the restriction enzyme PstI, have been cloned into the plasmid pBR322. One such fragment, which has its endpoints within phage genes T and C, carries the structural P2 int gene as well as its promoter and the phage att site. When introduced into a suitable bacterial host, the cloned fragment mediates the integration and excision of int- mutants of P2 and recombination within the phage att site in mixed infection. All these activities are independent of the orientation of the fragment within the plasmid. When introduced into minicells, the fragment produces, in addition to the products of genes D and U, a protein of 35-37,000 daltons identified as the int protein. A study of the map location of two amber int mutants, together with the sizes of the polypeptides they produce, indicates that the P2 int gene is transcribed from right to left on the P2 map, i.e. starting near gene C and proceeding toward att.

Chromosome Mapping↗
PubMed1982

Propagation of satellite phage P4 as a plasmid.

Satellite phage P4 has two known options for propagation. In its lytic cycle, its regulatory functions can act in trans to alter the actions of a helper virus (P2), which then provides necessary gene products, including capsid proteins. P4 also can be propagated in the absence of a helper as a prophage, with distinct sites for integration within the Escherichia coli chromosome. We determined that a single spontaneous mutation (vir1) of phage P4 allows a third mode of propagation: as a plasmid (along with continued integration into the host chromosome). Hence, the P4 regulatory element is capable of (i) temperate; (ii) lytic, helper-dependent; and (iii) plasmid modes of development. These findings emphasize the close relationship between defective viruses and plasmids.

Cloning, Molecular↗
PubMed1982

Exposure to toluene: concentration in subcutaneous adipose tissue.

Twelve male subjects were exposed to a toluene concentration of about 300 mg/m3 in the inspiratory air during rest and/or physical exercise on a bicycle ergometer. Each subject was exposed during four 30-min periods. Before exposure the subjects' body fat was calculated by means of underwater weighing and skeletal measurements. Needle biopsies of subcutaneous adipose tissue were taken up to 12 d after the exposure was concluded. The concentration of toluene in the adipose tissue was determined by gas chromatography after evaporation into nitrogen at a high temperature. After exposure at rest for 2 h, the mean concentration of toluene in adipose tissue was 0.7 mg (7.7 mumol)/kg. The corresponding value after 2 h of work at 50 W was 9.9 mg (109 mumol)/kg. There was a declining concentration of toluene in adipose tissue with an increasing degree of obesity. The half-time for toluene in adipose tissue ranged between 0.5 and 2.7 d. It increased with increasing amounts of body fat.

Adipose Tissue↗
PubMed1980

Cloning of the immunity repressor determinant of bacteriophage P2 in the pBR322 plasmid.

Through in vitro recombination of DNA restriction fragments, we have constructed a plasmid, which expressed in vivo the immunity repressor gene (C) of bacteriophage P2. A bacterial strain carrying such a plasmid showed a high level of P2 specific immunity. It was lysogenized normally by an infecting P2, but the frequency of spontaneous phage production was reduced about 10(4) fold as compared to a normal P2 lysogen. Satellite phage P4, known to derepress P2 lysogens, was unable to derepress the plasmid-carrying lysogenic strain so to allow growth of coinfecting P2. Phage P4 multiplied on the plasmid-carrying, P2-lysogenic strain, but due to a prolonged latent period failed to form plaques on this strain.

Cloning, Molecular↗
PubMed1979

A restriction endonuclease cleavage map of bacteriophage P2.

A restriction endonuclease cleavage map of phage P2 was constructed. The enzymes used and, within parenthesis, the number of their cleavage sites on the P2 lg cc DNA molecule were: AvaI(3), BalI(1), BAMI(3), BglII(3), HaeIII (more than 40; only three were mapped), HindIII(0), HpaI(10), KpnI(3), PstI(3), SalI(2) and SmaI(2). The EcoRI cleavage sites (3), as determined earlier, were used as reference points for this study. The DNAs of a variety of P2 mutants carrying chromosomal aberrations (dell, del2, del3, del6, vir22, vir37(2), vir79 and vir94) were also similarly examined.

Chromosome Aberrations↗
PubMed1978

Defective particle assembly in wild type P2 bacteriophage and its correction by the lg mutation.

The mutation lg of phage P2 has been located on the genetic map of P2 to the right of, and closely linked to, the del2 deletion, probably within tail gene F. The lg mutation causes larger burst sizes, compared with the wild type, especially at high incubation temperatures. The frequency of defective particles is lower in preparations of P2 lg than in those of wild type P2. It seems that the mutation lg improves the efficiency of particle assembly.

Coliphages↗
PubMed1977

State of prophage Mu DNA upon induction.

We have compared the process of prophage lambda induction with that of prophage Mu. According to the Campbell model, rescue of lambda DNA from the host DNA involves reversal of lambda integration such that the prophage DNA is excised from the host chromosome. We have monitored this event by locating the prophage DNA with a technique in which DNA of the lysogenic cells is cleaved with a restriction endonuclease and fractionated in agarose gels. The DNA fragments are denatured in gels, transferred to a nitrocellulose paper, and hybridized with 32P-labeled mature phage DNA. The fragments containing prophage DNA become visible after autoradiography. Upon prophage lambda induction, the phage-host junction fragments disappear and the fragment containing the lambda att site appears. No such excision is seen in prophage Mu. The Mu-host junction fragments remain intact well into the lytic cycle, when Mu DNA has undergone many rounds of replication and apparently many copies of Mu DNA have been integrated into the host DNA. Therefore, we postulate that Mu DNA replicates in situ and the replication generates a form of Mu DNA active in the integrative recombination between Mu DNA and host DNA. This type of mechanism may be common to many transposable elements.

Coliphages↗