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Biomedical subjects

M Severini

Publications and source records attributed to M Severini.

14 recordsLinked to original sources
PubMed2003

Sublethal effect of a weak intermittent magnetic field on the development of Xenopus laevis (Daudin) tadpoles.

In three repeated experiments with three different litters of Xenopus laevis (Daudin) tadpoles, three cohorts were reared in an aquarium under the "saw-tooth" magnetic field produced by a television set. Their maturation times are compared with those of three corresponding control cohorts grown in an unexposed aquarium. In the exposed aquarium, the magnetic field amplitude was less than 25 microT and the frequency in the extremely-low-frequency and very-low-frequency wavebands. Neither the exposed nor the unexposed cohorts suffered significant mortality and malformations. However, the exposed tadpoles took about 5 days more than the unexposed ones to reach metamorphosis. The differences in mean maturation times between the exposed and control cohorts were extremely significant (P < 0.001). The results show that a biological population can suffer a sublethal effect when exposed to the magnetic field of a TV set for a long time in the course of juvenile life stages, and that this effect can consist of a delay in reaching the adult stage.

Animals↗
PubMed1995

High-level expression of recombinant porcine LH receptor in baculovirus-infected insect cells or caterpillars.

Porcine LH receptor ectodomain was overexpressed in insect cells and lepidopteran larvae using the recombinant baculovirus expression system. A low multiplicity of infection yielded the largest active production, of approximately 10(7) receptors/cell or 3 micrograms active receptor/mg total protein in infected cells. The truncated ectodomain solubilized with Triton X-100 bound its ligand with a high affinity which was comparable with that of the native membrane receptor. Increasing the multiplicity of infection resulted in an optimum protein production of 0.6 mg receptor/mg total protein in infected cells. This receptor was largely inactive, probably trapped within aggregation pools. Active receptor could be recovered by dilution of the samples. No secretion of recombinant receptor was ever observed whatever the conditions of infection. Expression of the recombinant receptor in insect larvae was also tested. This low-cost system failed both to increase the amount of active receptor and to induce secretion into the haemolymph. Two methods remain for producing sizeable amounts of active receptor with this baculovirus/insect cell system. One relies on immunoaffinity purification of the active protein and requires large-scale production, and the other is based on the purification of overexpressed inactive receptor followed by renaturation.

Amino Acid Sequence↗
PubMed1995

Influence of promoter and signal peptide on the expression and secretion of recombinant porcine LH extracellular domain in baculovirus/lepidopteran cells or the caterpillar system.

Overexpression of the porcine LH receptor (pLHR) ectodomain has been achieved using the baculovirus-insect cell system but mostly in an aggregated form with no secretion. In order to carry this out, new baculoviruses were selected to produce the pLHR ectodomain in insect Sf9 cells and caterpillars. In pLHR-P10-297 and pLHR-mel-319 baculoviruses, pLHR cDNA was under the control of the P10 promoter and the polyhedrin gene promoter respectively. The constructs contained either the porcine signal peptide (pLHR-P10-297) or the insect signal peptide of melittin (pLHR-mel-319). Infected cells produced 1 x 10(5)-3 x 10(5) receptors/cell 3 days after infection. The recombinant LH receptor ectodomains produced were secreted in a biologically active form and bound the hormone with high affinity. Infected caterpillars produced a larger amount of active pLHR ectodomain that insect cells. The products were not secreted into the haemolymph however. Promoter and/or signal peptide modifications therefore enabled pLHR recombinant ectodomain secretion in a biologically active form, using the baculovirus-lepidopteran cell system. Moreover, moderate levels of expression seem to allow the production of biologically active ectodomain.

Animals↗
PubMed1992

Proteolysis of Bacillus stearothermophilus IF2 and specific protection by fMet-tRNA.

Translation initiation factor IF2 from Bacillus stearothermophilus (741 amino acids, Mr 82,043) was subjected to trypsinolysis alone or in the presence of fMet-tRNA. The initiator tRNA was found to protect very efficiently the Arg308-Ala309 bond within the GTP binding site of IF2 and, more weakly, three bonds (Lys146-Gln147, Lys154-Glu155 and Arg519-Ser520). The first two are located at the border between the non-conserved, dispensable (for translation) N-terminal portion and the conserved G-domain of the protein, the third is located at the border between the G- and C-domains. Since IF2 is known to interact with fMet-tRNA through its protease-resistant C- (carboxyl terminus) domain, the observed protection suggests that, upon binding of fMet-tRNA, long-distance tertiary interactions between the IF2 domains may take place.

Amino Acid Sequence↗
PubMed1991

Ribosome-independent GTPase activity of translation initiation factor IF2 and of its G-domain.

In the absence of ribosomes, Bacillus stearothermophilus translation initiation factor IF2 (Mr = 82 kDa) and its GTP-binding domain (i.e. the G-domain, Mr = 41 kDa) promote barely detectable hydrolysis of GTP. Upon addition of some aliphatic alcohols, however, the rate of nucleotide cleavage is substantially increased with both IF2 and G-domain, the highest stimulation being observed with 20% (v/v) ethanol. Under these conditions, the rates of ribosome-independent GTP hydrolysis with both IF2 and G-domain are approximately 30-fold lower than the corresponding rates obtained in the presence of ribosomes, while the Km for GTP is approximately the same in all cases. These results indicate that, as with the other two prokaryotic G proteins involved in translation (i.e. elongation factors EF-Tu and EF-G), also in the case of IF2, the GTPase catalytic center resides in the factor and, more specifically, in its G-domain.

Ethanol↗
PubMed1991

Molecular dissection of translation initiation factor IF2. Evidence for two structural and functional domains.

By means of limited proteolysis of Bacillus stearothermophilus initiation factor IF2 and genetic manipulation of its structural gene, infB, we have been able to produce (or hyperproduce) and purify two polypeptide fragments corresponding to two structurally and functionally separate domains of the protein. The first is the G-domain (approximately 41 kDa), which makes up the central part of the molecule and contains the conserved structural elements found in all GTP/GDP-binding sites of G-proteins. This domain is resistant to proteolysis in the presence of GTP or GDP, retains the capacity to interact with the 50 S subunit, binds weakly to the 30 S subunit, and displays ribosome-dependent GTPase activity with an approximately 2-fold higher Km for GTP and the same Vmax as compared with intact IF2. The second is the C-domain (approximately 24 kDa), which corresponds to the COOH-terminal part of IF2 and constitutes an extraordinarily compact domain containing the fMet-tRNA binding site of IF2. In spite of its negligible affinity for the ribosomes, the C-domain weakly stimulates the ribosomal binding of fMet-tRNA, presumably by affecting the conformation of the initiator tRNA molecule.

Amino Acid Sequence↗
PubMed1990

Proteolysis of Bacillus stearothermophilus IF2 and specific protection by GTP.

Translation initiation factor IF2 from Bacillus stearothermophilus (741 amino acids, Mr = 82,043) was subjected to trypsinolysis alone or in the presence of GTP. Following electroblotting and automated amino acid sequencing of the resulting peptides, the location and the sequential order of the main cleavage sites were identified. Trypsinolysis of IF2 ultimately generates two compact domains: a 24.5 kDa C-terminal fragment and a 40 kDa G-fragment which is obtained only in the presence of GTP which strongly protects a cleavage site within the GTP binding domain.

Amino Acid Sequence↗
PubMed1978

Epidemiologic study on enzootic bovine leukemia in Italy.

The results obtained from serologic and hematologic investigations conducted on 1.124 cattle belonging to 14 herds located in Central Italy are reported. The results demonstrate a considerable number of animals with antibodies to Bovine Leukemia Virus (BLV) and/or lymphocytosis, coming from Friesian herds with or without history of leucosis. Furthermore it is demonstrated the absence of animals with circulating antibodies to BLV in herds made up of the Chianina breed even with a herd history of leucosis.

Animals↗
PubMedDate not supplied

[Bovine enzootic leukemia and study of c-type particles in a cow with acute lymphatic leukemia and in cattle of the same herd with persistent lymphocytosis].

A case of acute lymphatic leukemia in a 7-month-pregnant Italian Friesian cow, aged about 6 years and belonging to a small dairy herd of 11 cows is described. Hematologic, histopatologic and ultrastructural examinations were performed, the ultrastructural studies were confined to the lymphnodes, thymus and buffy-coat cultures from peripheral blood. The remaining animals were subjected to hematologic examination and electron microscopy examination of buffy-coat cultures from peripheral blood. C-type particles were found in phytohemagglutinin (PHA)-treated and untreated buffy-coat cultures from the leukemic cow and from the animals with persistent lymphocytosis. C-type particles were also found in milk samples from 3 cows with persistent lymphocytosis.

Animals↗
PubMedDate not supplied

Epidemiologic study on enzootic bovine leukemia using serologic tests and hematologic examinations.

In order to find suitable diagnostic procedures to use in an epidemiologic survey for the detection of animals infected with the bovine leukemia virus (BLV), the authors conducted an investigation on 262 Friesian dairy cattle. The results of hematologic, serologic, and electron microscopic examinations are reported. Evaluation of the results demonstrated the validity of the immunodiffusion and immunofluorescence tests and the opportunity for their use in conjunction with examination of the blood picture. From the data reported it would appear useful to extend the investigation to the herds without history of lymphosarcoma.

Animals↗