PubMed Health⌕ Search

Biomedical subjects

L Paolozzi

Publications and source records attributed to L Paolozzi.

At least 37 records · Page 2Linked to original sources
PubMed1994

A novel illegitimate recombination event: precise excision and reintegration with the Mu gem mutant prophage.

The bacteriophage Mu is known to insert its DNA more or less randomly within the Escherichia coli chromosome, as do transposable elements, but unlike the latter, precise excision of the prophage, thereby restoring the original sequence, is not observed with wild-type Mu, although it has been reported with certain defective mutants. We show here that the mutant prophage Mu gem2ts can excise precisely from at least three separate loci -- malT, lac and thyA (selected as Mal+, Lac+ and Thy+, respectively). This excision occurs under permissive conditions for phage development, is observed in fully immune (c+) lysogens, and is independent of RecA and of Mu transposase. Mu gemts2 excision is invariably accompanied by reintegration of a Mu gem2ts prophage elsewhere in the chromosome. In the case of Mal+ revertants, this prophage is systematically located at 94 min on the E. coli chromosome. Mu gem2ts excision therefore sheds some light on the long-standing paradox of the lack of precise Mu excision.

Bacterial Proteins↗
PubMed1993

Interleukin-1 and naproxen down-regulate the expression of IL-1 receptors in cultured human rheumatoid synovial cells (HRSC).

Using affinity binding of [125I]-IL-1 alpha and Scatchard analysis, we demonstrate here that exposure of cultured synovial cells (HRSC) to NPX (10(-4) M) for 96 h decreased the binding of IL-1 by 20 to 35%. This effect results from a down-regulation of the IL-1 receptors without change in the apparent binding affinity (kD: 770 pM). Pretreatment of cultures with IL-1 alpha (500 pg/ml) reduced the total binding of [125I]-IL-1 alpha on HRSC by 65%, indicating that IL-1 decreases the expression of its own receptors.

Arthritis, Rheumatoid↗
PubMed1993

[A comparative controlled trial of 2 administration modalities of tiopronin in rheumatoid arthritis].

Thiopronin is a second line drug for rheumatoid arthritis with proven efficacy in controlled trials versus a placebo, D-penicillamine, or gold salts. This 4-month study was aimed mainly at comparing the efficacy and safety of two thiopronin regimens, i.e., 1 g/d for 2 weeks followed by 1.5 g/d (regimen A) versus 0.5 g/d for 1 month, 0.750 g/d during the second month, then 1 g/d (regimen B). Because earlier investigations have suggested a role for copper in the activity of D-penicillamine, a secondary goal of this study was to evaluate whether the clinical effects of thiopronin were related to changes in serum copper and ceruloplasmin levels. Among the 61 included patients, 32 received regimen A and 29 regimen B. The primary efficacy criterion was the physician's overall efficacy assessment. Efficacy was rated good or excellent in 65.5% of regimen A patients and 55.6% of regimen B patients. Eighteen of the 32 regimen A patients and 23 of the 29 regimen B patients experienced at least one adverse event (p = 0.055). Failure to tolerate the drug required withdrawal in 12 of the 32 regimen A patients (37.5%) versus 11 of the 29 regimen B patients (37.9%). Declines in serum copper and ceruloplasmin levels were not correlated with treatment efficacy or tolerance. These findings, together with previously reported data, suggest that treatment should be initiated in a dosage of 1 g/day and that thiopronin-related adverse events are not dose-dependent.

Adult↗
PubMed1991

Global changes in gene expression in Escherichia coli K12 induced by bacteriophage Mu Gem protein.

We have studied the growth properties of some Mu lysogens with respect to the non-lysogenic strain and have observed that the division time in minimal medium was increased over 4-fold when the bacteria carried the prophage mutated in the gem gene (Mu gem3). Since this phage gene has previously been shown to be involved in modulation of expression of host genes, we have analysed the proteins extracted from lysogens and non-lysogens as a rapid assay of global gene expression. The pattern of proteins extracted showed marked quantitative variations between non-lysogens, lysogens for wild-type Mu and lysogens for phage Mu gem3. These effects were no longer as evident when the strains were grown in rich medium. This dramatic change in the physiological state of the lysogenic strain versus the non-lysogenic in particular growth conditions extends the concept of lysogeny. For many years, the prophage has been considered only as a potentially lethal factor, while here it also appears as a genetic element capable of profoundly modifying host biology.

Animals↗
PubMed1991

A class of gyrB mutants, substantially unaffected in DNA topology, suppresses the Escherichia coli K12 ftsZ84 mutation.

Previous work in our laboratory suggested that DNA topology could be implicated in the regulation of the division gene ftsZ. To settle this question, we have selected and characterized mutants in the gyrB gene able to phenotypically suppress the defects of the ftsZ84 mutation. No strict correlation was found between the degree of plasmid DNA relaxation and the level of suppression of the thermosensitivity of the ftsZ84 strain. Interestingly, the class of mutants that shows maximal suppression is substantially unaffected in DNA topology. In addition, the amount of ftsZ-specific mRNA in this class of mutants is comparable to that present in the ftsZ84 strain. These results hint that the ability of these gyrB mutants to correct the effects of the ftsZ84 mutation is largely unrelated to the function of the GyrB (as a part of DNA gyrase) in the control of DNA superhelicity and suggest hitherto unsuspected interaction between the ftsZ and gyrB gene products.

Bacterial Proteins↗
PubMed1991

[Decrease of the functional affinity of rheumatoid factors under the effect of tiopronin].

Sixteen rheumatoid arthritis patients were serologically examined, before and after a 2-month treatment with tiopronine (TP). The titer of agglutinating rheumatoid factor (RF) as well as the level of non-agglutinating RF were significantly reduced in serum and synovial fluid (SF). The functional affinity of the remaining RF was attenuated in serum (p less than 0.01) and SF (p less than 0.05). Conversely, the proportion of asialylated IgG was enhanced in serum (p less than 0.05) and SF (p less than 0.05). These findings would suggest that TP might restore the efficacity of sialyl transferase at the B lymphocyte level.

Adult↗
PubMed1990

Mu gem3 as a tool to investigate the influence of chromosome supercoiling on gene expression in Escherichia coli K12.

We have developed a rapid method to investigate the influence of chromosome supercoiling on gene expression in Escherichia coli K12. This method exploits the ability of the gem3 mutant of the bacteriophage Mu, even in the prophagic state in immune cells, to induce relaxation of the host chromosome. The experiments can thus be performed under physiological conditions, and without the use of the drugs. In theory, this method can be applied to any bacterial gene. Here, we report the results obtained with four DNA replication and three cell division genes.

Bacteriophage mu↗
PubMed1990

The bacteriophage Mu gem gene: a positive regulator of the C operon required for normal levels of late transcription.

The gem product of bacteriophage Mu modulates synthesis of various host proteins and alters the host chromosome topology. To elucidate the role of the gem gene in Mu development, we analyzed the behavior of several mutants in this gene. The results, obtained with two Mu gem- phages, show that (1) phage growth is significantly delayed and inhibited, (2) early transcription is normal but late transcription is delayed and reduced, (3) DNA replication appears normal, and (4) the Mu C gene, whose product positively regulates Mu late genes, is one of the gem target sites. Transcription of a C promoter-lacZ fusion, carried by the pPH91 plasmid, is stimulated both after infection with Mu gem+ or Mu gem3 and is strains lysogenic for the same phages in the presence of viral immunity. These data suggest that the primary role of the gem product is modulation of gene expression. This control could be carried out by direct interaction with transcription factors or by changing DNA supercoiling.

Bacteriophage mu↗
PubMed1989

Synchronous division induced in Escherichia coli K12 by gemts mutants of phage Mu.

Infection with the bacteriophage mutant Mu c+ gemts2 at 42 degrees C induces synchrony in cell division in cultures of Escherichia coli K12. This synchrony may last for several cycles and is not only due to selection since synchronization is observed even when bacterial survival to the infection is over 80% as in lysogens for Mu c+ gemts2. The mechanism by which synchrony is induced is not known, but since the product of Mu gene gem (previously called lig) has been shown to interact with the enzymatic system in the bacteria controlling the degree of DNA supercoiling, the phenomenon could be a consequence of this interaction.

Ampicillin Resistance↗
PubMed1989

Suppression of the thermosensitive DNA ligase mutations in Escherichia coli K12 through modulation of gene expression induced by phage Mu.

We have previously shown that Mu can sustain the growth at non-permissive temperature of an Escherichia coli strain harbouring a thermosensitive mutation in the DNA ligase structural gene. This "complementation" reaches a maximal level with the Mu lig3 mutant which restores the viability of a ligts7 strain to the level of the wild type (Ghelardini et al. 1980; Paolozzi et al. 1980). In this study we analysed the characteristics of this phenotypic suppression in order to clarify its molecular mechanism. We found that an E. coli ligts7 strain lysogenic for the Mu lig3 mutant shows: (i) an increment in the host DNA ligase activity; (ii) an increase in the specific mRNA of the host lig gene; (iii) an increase (towards the relaxed state) in the average linking number of a resident plasmid; and (iv) a reduction in DNA gyrase activity. These results are compatible with the hypothesis that the Mu lig gene product by interfering with the host enzymatic apparatus controlling DNA topology leads to a reduction in chromosomal supercoiling. The relaxation of the chromosome could affect the transcription of the DNA ligase gene, amongst others. Thus, through this mechanism, the Mu lig gene product is able to modulate gene expression and hence suppress the effects of the E. coli ligts7 mutation. On the basis of the identification of this mechanism of action, we propose to change the name of the Mu lig gene (thought originally to be the structural gene for a bacteriophage ligase) to gem (gene expression modulation).

Bacteriophage mu↗
PubMed1989

The expression of the DNA ligase gene of Escherichia coli is stimulated by relaxation of chromosomal supercoiling.

Many genes of Escherichia coli have been shown to be sensitive to DNA superhelicity. The superhelicity of the chromosome is itself also supercoiling-dependent. We have developed a general strategy for investigating how a particular gene responds to changes in DNA topology. This approach is used to study the E. coli ligase gene. The thermosensitivity of the E. coli ligts251 mutation can be phenotypically suppressed by mutations which map close to, or in, the gyrB gene and which affect the degree of DNA supercoiling. The level of suppression correlates with the degree of DNA relaxation observed, suggesting that the gene encoding the E. coli DNA ligase is activated by relaxation of the chromosomal DNA.

Chromosomes, Bacterial↗
PubMed1986

General method for the isolation of conditional lethal mutants in any required region of the virus genome: its application to the 'semi-essential' region of phage Mu.

A general method is presented that enables viral mutants to be isolated in any required region of their genome. An application of the method is reported relating to the isolation of conditional lethal mutants in the "semi-essential' region of phage Mu. Some properties are described of one mutant found in this way, Mucts62SEEam8 Apl, which is typical of a class of mutants that were isolated.

Bacteriophage mu↗
PubMed1984

Escherichia coli K-12 gyrB gene product is involved in the lethal effect of the ligts2 mutant of bacteriophage Mu.

Mu ligts2 mutants, defective for development and integration, show a high killing effect on the infected host. A number of survivors to Mu ligts2 infection were analyzed; they are characterized by nonpermissivity for both development and lysogenization of bacteriophage Mu. Bacteriophages D108 and P1 are also inhibited in these strains as is transposon Tn9. The corresponding mutation site was mapped at 82 min and identified with the Escherichia coli gyrB site.

Coliphages↗
PubMed1982

Conservative integration of bacteriophage Mu DNA into pBR322 plasmid.

In order to clarify the first step in Mu integrative recombination, we have infected a bacterial strain harboring the plasmid pBR322 and isolated Mu DNA in a supercoiled form associated with this plasmid. These structures show an association of Mu with PBR322 without any preliminary replication.

Bacteriophage mu↗
PubMed1980

Two classes of Mu lig mutants: the thermosensitives for integration and replication and the hyperproducers for ligase.

We have previously shown that Mu restores an active DNA replication at non-permissive temperature in E. coli K12 ligts7 strains. In this paper we describe two new types of phage mutants for the Mu lig function. The Mu ligts mutants are conditional lethals defective for both integration and replication of DNA, unable to 'complement' the bacterial lig mutation; the map between B and lys. The mutants of the other type, on the other hand, are able to restore to a maximum level the activity impaired by the ligts7 mutation in the host. We suggest the hypothesis that the product of Mu lig gene could be part of a complex as a topoisomerase.

Chromosome Deletion↗