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Biomedical subjects

L Bossi

Publications and source records attributed to L Bossi.

At least 55 records · Page 3Linked to original sources
PubMed1983

Context effects: translation of UAG codon by suppressor tRNA is affected by the sequence following UAG in the message.

The efficiency of various suppressor tRNAs in reading the UAG amber codon has been measured at 42 sites in the lacI gene. Results indicate that: (1) for all suppressors, efficiency is not an a priori value; rather, it is determined at each site by the specific reading context of the suppressed codon; (2) the degree of sensitivity to context effects differs among suppressors. Most affected is amber suppressor supE (su2), whose activity varies over a 20-fold range depending on context; (3) context effects are produced by residues present at the 3' side of the UAG codon. The most important role appears to be played by the base that is immediately adjacent to the codon. When this base is a purine, the amber codon is suppressed more efficiently than when a pyrimidine is in the same position. Superimposed on this initial pattern, the influence of bases further downstream to the UAG triplet can be detected also. The possibility is discussed that context effects are produced by the whole codon following UAG in the message.

Base Sequence↗
PubMed1983

The hisR locus of Salmonella: nucleotide sequence and expression.

In S. typhimurium, the hisR locus is defined by mutations causing reduced levels of the histidine transfer RNA. As a preliminary step in the analysis of the hisR mutants, a 972 bp DNA fragment containing the histidine tRNA gene from wild-type Salmonella was cloned and completely sequenced. This analysis revealed the existence of a tRNA gene cluster which, in addition to the tRNAHis gene, includes the genes for tRNALeu1, tRNAPro1 and a tentative tRNAArgCGG. All four tRNA genes are present as single copies and are separated by spacer sequences ranging from 20 to 53 bp in length. The gene cluster is efficiently transcribed in vitro by E. coli RNA polymerase and yields a transcript, approximately 480 nucleotides long, which contains all four tRNA sequences. This tetrameric precursor can be processed to 4S RNA in vitro with a wild-type Salmonella extract, but not with an extract prepared from a hisU (RNase P) mutant. Using portions of the tRNA gene cluster as specific hybridization probes, various processing intermediates were shown to accumulate in vivo in the hisU mutant. Most of these RNAs are monomeric precursors only a few nucleotides longer than the respective mature tRNA species.

Base Sequence↗
PubMed1983

New suppressors of frameshift mutations in Salmonella typhimurium.

Several new types of suppressor mutants have been isolated. These were identified among revertants of mutants originally generated by mutagens other than the acridine-derived ICR191. The new suppressors correct mutations other than those with runs of C or G which are recognized by the previously described suppressors. Several frameshift mutations are corrected by more than one suppressor type. Apparently, the DNA base sequence near these mutant sites includes sites of action for several distinct suppressor types.

Base Sequence↗
PubMed1983

Genetic characterization of the sufj frameshift suppressor in Salmonella typhimurium.

A new suppressor of +1 frameshift mutations has been isolated in Salmonella typhimurium. This suppressor, sufJ, maps at minute 89 on the Salmonella genetic map between the argH and rpo(rif) loci, closely linked to the gene for the ochre suppressor tyrU(supM). The suppressor mutation is dominant to its wild-type allele, consistent with the suppressor phenotype being caused by an altered tRNA species. The sufJ map position coincides with that of a threonine tRNA(ACC/U) gene; the suppressor has been shown to read the related fourbase codons ACCU, ACCC, ACCA.--The ability of sufJ to correct one particular mutation depends on the presence of a hisT mutation which causes a defect in tRNA modification. This requirement is allele specific, since other frameshift mutations can be corrected by sufJ regardless of the state of the hisT locus.--Strains carrying both a sufJ and a hisT mutation are acutely sensitive to growth inhibition by uracil; the inhibition is reversed by arginine. This behavior is characteristic of strains with mutations affecting the arginine-uracil biosynthetic enzyme carbamyl phosphate synthetase. The combination of two mutations affecting tRNA structure may reduce expression of the structural gene for this enzyme (pyrA).

Base Sequence↗
PubMed1983

Plasma levels of primidone and its metabolite phenobarbital: effect of age and associated therapy.

The effects of age and associated therapy on plasma primidone (PRM) and derived phenobarbital (PB) concentrations, and on plasma concentrations-to-PRM dose ratios (L/D ratio) were evaluated retrospectively from 408 consecutive PRM and derived PB determinations in 238 chronically treated epileptic patients (153 children and adolescents between 5 months and 15 years of age and 85 adults between 16 and 55 years of age). The correlation between PRM administered and both plasma PRM and derived PB levels was significant; the correlation between PRM and PB plasma levels was also significant, but the scatter of values for the linear regressions was such that the relationship had no predictive value. Significant differences in mean plasma PRM and PB L/D ratios were found between patients aged 0-3 years, 4-9 years, 10-15 years, and adults (16-55 years), with higher values in the older groups. The PB/PRM concentration ratios were significantly lower in children than in adolescents and adults. Concomitant treatment with carbamazepine affected PRM disposition and led to increased L/D ratios for PB and decreased L/D ratios for PRM, whereas phenytoin increased the L/D ratios for PB without any significant change in the L/D ratios for PRM. The variability in the results indicates the need for routine monitoring of PRM and derived PB plasma levels, particularly in pediatric populations, in order to tailor the dose to each patient.

Adolescent↗
PubMed1983

Double-blind crossover trial of progabide versus placebo in severe epilepsies.

In this double-blind, two-period, crossover trial with randomized treatment assignment, progabide (+/- 30 mg/kg/day) and placebo were compared as add-on to standard therapy in 20 "therapy-resistant" epileptic patients (11 males, nine females; age range, 7-47 years). The duration of each treatment period was 6 weeks. Crossover was performed gradually over 3-4 days. Twenty-four patients entered the study: three dropped out for reasons unrelated to progabide effects; one dropped out during the placebo period because of increased seizure frequency. Of the 20 patients who completed the study, 14 had partial, two partial plus secondary generalized, and four generalized seizures. Preexisting antiepileptic treatment consisted of one antiepileptic drug (AED) in three, two AEDs in eight, three AEDs in five, and four AEDs in four patients (mean, 2.5 AEDs/patient). The following parameters were recorded at biweekly intervals: (a) efficacy parameters--total seizure count, counts of each seizure type, and global clinical judgment; (b) safety parameters--adverse drug effects, brief clinical and neurological examinations, and laboratory tests; and (c) plasma concentrations of progabide and of the associated AEDs. Twelve patients were considered to be improved (p less than 0.01) with progabide by global clinical judgment compared with two patients improved with placebo. Nine patients of 20 had a 48-100% reduction of total seizure count in the verum period, leading to a significant reduction of total seizure number and of complex partial seizures in the verum period as compared with the placebo period (p less than 0.05). Adverse effects were reported or observed in 10 patients during the progabide period and in five patients in the placebo period. The side effects were generally mild and consisted of somnolence in four cases and of tremors, dry mouth, troubles of equilibrium, anorexia, euphoria, depression, and anxiety in individual patients; a 15-20% reduction of the progabide dose was required in two cases only. No treatment-related alterations in results of laboratory tests were observed.

Adolescent↗
PubMed1983

Indications for the use of gamma-aminobutyric acid (GABA)-agonists in convulsant disorders.

From studies using pharmacological models of convulsive disorders and also from the neurochemical analysis of epileptogenic tissue removed during neurosurgical resection (cortectomy), there is strong evidence that at least a subgroup of epileptic disorders may be linked (among other things) to a deficit in GABAergic neurotransmissions. This deficit may be found at the level of GABA synthesis or at the GABA-recognition site; whether these GABA neurons are lost or are dysfunctional is not yet answered. This suggests that GABA-agonists will be of potential use in epilepsy. GABA-agonists (progabide, SL 75102, muscimol, THIP) for the classical GABA-recognition sites as well as other compounds active at sites in the GABA-receptor macromolecular complex (eg, diazepam and phenobarbital) exhibit a wide range of anticonvulsant effects in different animal models and species. However, for some of these compounds (eg, muscimol) secondary central effects occur at the same dose level as the anticonvulsant actions, and for others (eg, THIP) such secondary effects may limit the use to certain types of seizures. This problem may be related to the high affinity of such compounds for the GABA recognition site as compounds with a more moderate affinity (eg, progabide, SL 75102) have a wider margin between anticonvulsant and secondary central effects in rodents. Clinical results using progabide suggests that the GABA hypothesis of convulsive disorders has indeed a rational foundation as a significant percent of refractory or unresponsive epileptic patients with different types of seizures (eg, complex partial or primary generalized) have a significant clinical improvement with this GABA-agonist.

Animals↗
PubMed1982

[Cerebral concentrations of anticonvulsants in patients with epilepsy of tumoral origin (author's transl)].

(1) The concentrations of various anticonvulsants (PB, PHT, CBZ, VPA) were measured in brain specimens from 7 patients who had undergone neurosurgery for a therapy resistant epilepsy of tumoral origin (astrocytoma) in 6 cases, glioblastoma in 1 case). (2) Great interindividual variability of the mean brain/plasma concentration ratios was observed for PB in 5 patients (range: 0.4-1.0). A mean brain/plasma ratio of 1.0 was recorded for PHT and CBZ (one patient each). (3) In the different tissue specimens (7-14) from the same patient AED concentrations varied greatly, even in neighboring areas. (4) Intraindividual variations were more marked in the present group of patients than in previously studied non-tumoral epileptics. (5) No correlation was found between the localization of the lesions and the variations in AED concentrations. (6) Brain AED concentration appeared to be higher in the few samples of non-tumoral tissue and lower in the 'epileptogenic' areas as defined by stereo-EEG seconding. (7) On the basis of these data, the hypothesis can be formulated that the therapy resistance of these patients may be at least partly explained by the presence of low AED concentration (even in presence of 'therapeutic' AED plasma levels) in the epileptogenic areas.

Adolescent↗
PubMed1982

[Motor and postural manifestations of temporal lobe epilepsy seizure].

This study reports on 73 epileptic seizures (in 36 patients) originating in the temporal lobe (stereo-EEG) presenting motor or postural signs. Motor symptoms occur rarely in the early phase of seizures (less than 10% of our series) and they are exceptional during spontaneous seizures. The critical electrical discharge always affects extra-temporal structures such as the rolandic operculum, the cingulate gyrus, etc. The occurrence of motor symptoms during the late phase of seizures is associated with a long duration of the critical discharge and, again, with the involvement of extra-temporal structures. The characteristics of the associated clinical signs (e.g., frequent loss of contact with the environment, relatively rare oroalimentary automatic activities), together with the high frequency of secondary 'generalizations' are consistent with the stereo-EEG findings and indicate that these seizures also affect extra-temporal regions.

Adolescent↗
PubMed1981

Determination of 5-hydroxytryptophan, serotonin and 5-hydroxyindoleacetic acid in rat and human brain and biological fluids by reversed-phase high-performance liquid chromatography with electrochemical detection.

A rapid and sensitive method for the concurrent determination of 5-hydroxytryptophan, serotonin and 5-hydroxyindole acetic acid by reversed-phase high-performance liquid chromatography with electrochemical detection has been developed. The separation of the indolic compounds was achieved using a phosphate-citric acid eluent containing 5% methanol. Detection limits in the low picogram range were found. The method has been applied to the determination of the indolic compounds in rat and human brain tissues, as well as in human plasma and cerebrospinal fluid. Tissue and plasma preparation required only deproteinization before chromatography, while cerebrospinal fluid was directly applied to the column.

5-Hydroxytryptophan↗
PubMed1981

Four-base codons ACCA, ACCU and ACCC are recognized by frameshift suppressor sufJ.

The frameshift suppressor sufJ acts to correct a set of +1 frameshift mutations having very different sequences at their mutant sites. This suppressor acts by reading a 4 base codon located near, but not at, the site of each suppressible mutation. Suppression thus necessitates out-of-phase translation of the short stretch of mRNA between the site of action of the suppressor tRNA and the site of the frameshift mutation. We have identified the site read by sufJ by mutationally creating a series of such sites in the neighborhood of a previously nonsuppressible frameshift mutation. Each of the newly generated sites was formed by base substitution. Four independently generated sites were analyzed by DNA sequencing. At each site the quadruplet codon ACCX was generated (where X is A, U or C). Thus sufJ is able to read a 4 base codon in which any of three bases is acceptable in the fourth position. This is the first frameshift suppressor that does not read a run of three repeated bases in the first three positions of its codon.

Base Sequence↗
PubMed1980

The influence of codon context on genetic code translation.

A class of mutations that increase the deficiency of a suppressor tRNA in translating a particular amber codon has been characterized. The increased efficiency is due to a mutation resulting in a change in the mRNA that affects the nucleotide adjacent to the 3' side of the UAG triplet. Thus the interaction of tRNA with mRNA is influenced by mRNA sequences outside the triplet codon.

Base Sequence↗
PubMed1980

Model for regulation of the histidine operon of Salmonella.

A model is proposed that accounts for regulation of the histidine operon by a mechanism involving alternative configuration of mRNA secondary structure (the alternative stem model). New evidence for the model includes sequence data on three regulatory mutations. The first (hisO1242) is a mutation that deletes sequences needed to form the attenuator mRNA stem and causes constitutive operon expression. The second mutation (hisO9654) is a His- ochre (UAA) mutation in the leader peptide gene; the existence of this mutation constitutes evidence that the leader peptide gene is translated. The third mutation (hisO9663) is remarkable. It neither generates a nonsense codon nor affects a translated sequence; yet, it is suppressible by amber suppressors. We believe this mutation causes a His- phenotype by interfering with mRNA secondary structure. The suppressibility of the mutation is probably due to disruption of the attenuator stem by ribosomes that read through the terminator codon of the leader peptide gene. This explanation is supported by the observation of derepression of a wild-type control region in the presence of an amber suppressor. Evidence is presented that hisT mutants (which lack pseudouridine in the anticodon arm of histidine tRNA) may cause derepression of the his operon by slowing protein synthesis in the leader peptide gene.

Bacterial Proteins↗
PubMed1980

Effect of L-5HTP and drugs acting on serotonin metabolism in various myoclonic syndromes.

Ten patients affected by various myoclonic syndromes were tested with drugs acting on cerebral serotonin metabolism and with clonazepam (CZP). After L5HTP or serotonergic drugs administration a clear cut improvement was observed in the 2 patients affected by Ramsay-Hunt syndrome, while the patients with myoclonic epilepsy have shown no effect (3 cases) or negative response (1 case). Methysergide was active only in 1 patient affected by progressive erratic myoclonus who had a striking worsening of clinical picture. The main side effects observed were: gastrointestinal distress (L5HTP--4 patients, fenfluoramine--2, quipazine--1, methysergide--2) and cutaneous rash (quipazine--1 case). These results support the possible implication of the serotonergic system in the pathogenesis of myoclonus other than post-anoxic.

5-Hydroxytryptophan↗