Biomedical subjects

F Spirito

Publications and source records attributed to F Spirito.

At least 19 recordsLinked to original sources

PubMed2006

Nondisjunction rates of mouse chromosomes involved in heterozygous Rb rearrangements measured by chromosome painting of spermatocytes. II. The effects of trivalent combinations and genetic background.

Chromosome specific nondisjunction rates were quantified by dual-colour FISH in spermatocytes II of Robertsonian heterozygous mice with different trivalent combinations or, alternatively, with different genetic backgrounds. We found that such factors do not influence the proneness to nondisjunction of specific chromosomes.

Animals↗

PubMed2005

A randomized controlled trial of pegylated interferon alpha-2a (40 KD) or interferon alpha-2a plus ribavirin and amantadine vs interferon alpha-2a and ribavirin in treatment-naïve patients with chronic hepatitis C.

We determined whether triple therapy comprising amantadine (AMA), ribavirin (RBV) and either peginterferon (PEG-IFN) alpha-2a or conventional IFN alpha-2a would improve sustained virological response (SVR) rates over dual therapy with IFN alpha-2a and RBV in patients with chronic HCV infection. A total of 362 treatment-naïve patients were randomized to 48 weeks of treatment with: PEG-IFN alpha-2a 180 microg/week (group A) or IFN alpha-2a 3 MU tiw (groups B and C). All patients received RBV 1000 or 1200 mg/day and those in groups A and B received AMA 200 mg/day. SVR was defined as an undetectable HCV RNA after 24 weeks of untreated follow-up. At the end of therapy, 74.4% (95% CI 0.66-0.82) of patients in group A were HCV RNA-negative compared with 42.5% (95% CI 0.33-0.50) of those in group B (P = 0.0001) and 48.8% (95% CI 0.40-0.56) of those in group C. SVR was achieved in a significantly greater proportion of patients in group A compared with groups B and C: 65.3% (95% CI 0.53-0.56), 33.3% (95% CI 0.25-0.41) and 44.6% (95% CI 0.36-0.53; P = 0.0001) respectively. In patients with genotype 1, SVR rates were 55.2, 22.8 and 28.8% with the three regimens respectively. Factors independently associated with SVR were HCV genotype 2 or 3, therapy with PEG-IFN, female gender and age. In treatment-naive patients with chronic hepatitis C, triple therapy with PEG-IFN alpha-2a, RBV and AMA produces higher SVR than dual or triple therapy with conventional IFN alpha-2a.

Adolescent↗

PubMed2004

Nondisjunction rates of mouse specific chromosomes involved in heterozygous Rb rearrangements measured by chromosome painting of spermatocytes II. I. The effects of the number of trivalents.

Dual-colour FISH painting with alternative fluorescent chromosome-specific probes allowed us to distinguish chromosomes 1, 4, 6 and 14. The purpose was to check whether nondisjunction rates of specific chromosomes involved in heterozygous Robertsonian fusions are independent of the number of trivalents, or an epistatic effect among Rb chromosomes takes place affecting nondisjunction rates. Probes were used on DAPI-stained metaphases of spermatocytes II of laboratory strains of mice with reconstructed karyotypes heterozygous for one, two, three or four Robertsonian metacentrics in an all-acrocentric background. The existence of such epistatic interactions was not verified.

Aneuploidy↗

PubMed2003

Cerebellar contribution to spatial event processing: do spatial procedures contribute to formation of spatial declarative knowledge?

Spatial knowledge of an environment involves two distinct competencies: declarative spatial knowledge, linked to where environmental cues are and where the subject is with respect to the cues, and, at the same time, procedural spatial knowledge, linked to how to move into the environment. It has been previously demonstrated that hemicerebellectomized (HCbed) rats are impaired in developing efficient exploration strategies, but not in building spatial maps or in utilizing localizing cues. The aim of the present study was to analyse the relationships between spatial procedural and declarative knowledge by using the open field test. HCbed rats have been tested in two different protocols of the open field task. The results indicate that HCbed animals succeeded in moving inside the arena, in contacting the objects and in habituating to the new environment. However, HCbed animals did not react to environmental changes, when their impaired explorative pattern was inappropriate to the environment, suggesting that they were not able to represent a new environment because they were not able to explore it appropriately. Nevertheless, when their altered procedures were favoured by object arrangement, they detected environmental changes as efficiently as did normal rats. This finding suggests that no declarative spatial learning is possible without appropriate procedural spatial learning.

Animals↗

PubMed2003

Cosegregation of Robertsonian metacentric chromosomes in the first meiotic division of multiple heterozygous male mice as revealed by FISH analysis of spermatocyte II metaphases.

Contrasting results (random segregation or cosegregation of isomorphic chromosomes) have been reported up to now on the segregation pattern of Robertsonian metacentric chromosomes of Mus musculus domesticus in multiple heterozygotes, using different approaches (karyotypical analysis of the progeny or of second meiotic metaphases). In the present contribution data are presented based on FISH (Fluorescence In Situ Hybridisation) analysis with telomeric probes, which allowed us to distinguish metacentric chromosomes from pairs of acrocentric chromosomes with their centromeric regions close to each other. Probes were hybridized to DAPI stained metaphases of spermatocytes II of mice heterozygous for two, three or four Robertsonian metacentrics in an all-acrocentric background, the karyotype of which has been reconstructed starting from laboratory strains. Isomorphic chromosomes tend to cosegregate (metacentrics with metacentrics, acrocentrics with acrocentrics); the values found for cosegregation have a clear even if moderate effect on the reproductive isolation caused by underdominant chromosomal rearrangements.

Animals↗

PubMed2002

Partial deletions of long arm of chromosome 6: biologic and clinical implications in adult acute lymphoblastic leukemia.

Within 285 adult acute lymphoblastic leukemias (ALL) included in the multicenter GIMEMA 0496 trial and prospectively studied by conventional cytogenetics, 18 cases (6%) with long arm deletion of chromosome 6 (6q) were identified. These cases were divided into: (i) del(6q) only (n = 6); (ii) del(6q) plus other numerical and/or structural abnormalities (n = 8); (iii) del(6q) and other 'specific' translocations (n = 4). The biologic and clinical features of the patients carrying this anomaly, as well as their outcome, were compared with those of 267 patients without del(6q). A T cell phenotype was more frequently associated with del(6q) cases in general (P = 0.001) and particularly with cases presenting del(6q) as the isolated abnormality (P = 0.0027). No significant difference with respect to multidrug resistance (MDR)/P glycoprotein expression was observed between the two groups of patients (21% vs 28% of MDR-positive cases, respectively). A BCR-ABL fusion transcript was less frequently detected in cases with del(6q) (11%) compared with those without the anomaly (29%). p15 and p16 deletions were identified by Southern blot analysis in 21% of cases with del(6q) and in 26% of cases without del(6q). In this latter group, a T cell phenotype was less frequently associated with p15 and/or p16 deletion than in the group carrying del(6q) (36% vs 100% of cases, P = 0.011). Overall, patients with ALL and del(6q) had a high complete remission (CR) rate (83%); however, they had a lower 18 month event-free survival (31% vs 41%) and a higher relapse rate (70% vs 37%, P = 0.02) compared with patients without del(6q). To date, this is the largest series of adult ALL cases reported with del(6q) homogeneously treated, which have also been prospectively studied for MDR expression and for the detection of known fusion genes. This anomaly, as an isolated change, identifies a subset of cases with hyperleukocytosis (median WBC count 52 x 10(9)/l) and a strict correlation with a T cell phenotype. Overall, del(6q) seems to be associated with an unfavorable clinical outcome, although this finding will need to be confirmed by extended FISH analysis.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

The short arm of the laminin gamma2 chain plays a pivotal role in the incorporation of laminin 5 into the extracellular matrix and in cell adhesion.

Laminin 5 is a basement membrane component that actively promotes adhesion and migration of epithelial cells. Laminin 5 undergoes extracellular proteolysis of the gamma2 chain that removes the NH(2)-terminal short arm of the polypeptide and reduces the size of laminin 5 from 440 to 400 kD. The functional consequence of this event remains obscure, although lines of evidence indicate that cleavage of the gamma2 chain potently stimulated scattering and migration of keratinocytes and cancer cells. To define the biological role of the gamma2 chain short arm, we expressed mutated gamma2 cDNAs into immortalized gamma2-null keratinocytes. By immunofluorescence and immunohistochemical studies, cell detachment, and adhesion assays, we found that the gamma2 short arm drives deposition of laminin 5 into the extracellular matrix (ECM) and sustains cell adhesion. Our results demonstrate that the unprocessed 440-kD form of laminin 5 is a biologically active adhesion ligand, and that the gamma2 globular domain IV is involved in intermolecular interactions that mediate integration of laminin 5 in the ECM and cell attachment.

Basement Membrane↗

PubMed2001

Reduced expression of the epithelial adhesion ligand laminin 5 in the skin causes intradermal tissue separation.

Laminin 5, the major keratinocyte adhesion ligand, is found in the lamina lucida subregion of the epidermal basement membrane of the skin, where it colocalizes with the anchoring filaments. Mutations in the genes encoding laminin 5 cause junctional epidermolysis bullosa, an inherited skin blistering disease characterized by abnormal hemidesmosomes and cleavage of the lamina lucida leading to epidermal detachment. In this work we describe the genetic basis of a new subtype of lethal inherited epidermolysis bullosa associated with reduced skin reactivity to laminin 5, presence of mature hemidesmosomes, and intradermal cleavage of the skin. The epidermolysis bullosa patients were heterozygous for a nonsense mutation (Q896X) and a splice site mutation (764-10T-->G) in the gene (LAMC2) for the gamma2 chain of laminin 5. The nonsense mutation causes accelerated decay of the corresponding mRNA, while the splice site mutation results in maturation of a cryptic wild-type gamma2 mRNA leading to reduced expression of wild-type laminin 5. In vitro studies using the probands' keratinocytes showed that secretion of reduced amounts of functional laminin 5 in the patient, although permitting formation of hemidesmosomes, fail to restore efficient cell adhesion. Our results provide the first evidence that laminin 5 contributes to the firm adhesion of the epithelial basement membrane to the underlying stroma. They also show that a low expression level of laminin 5 induces assembly of mature hemidesmosomes in vivo but fails to assure a stable cohesion of the dermal-epidermal junction.

3T3 Cells↗

PubMed2001

Novel mutations in the LAMC2 gene in non-Herlitz junctional epidermolysis bullosa: effects on laminin-5 assembly, secretion, and deposition.

Laminin-5 is the major adhesion ligand of epithelial cells. Mutations in the three genes (LAMA3, LAMB3, LAMC2) encoding the laminin-5 chains cause junctional epidermolysis bullosa, a clinically and genetically heterogeneous blistering skin disease. Here, we describe a non-Herlitz junctional epidermolysis bullosa patient, compound heterozygote for two novel mutations affecting the LAMC2 gene. The mutation in the paternal allele is a de novo splice site mutation (522-1G-->A) that results in in-frame skipping of exon 4 and synthesis of a mutated gamma2 polypeptide (gamma2Delta4) carrying a 33 amino acid deletion within the N-terminal domain V. The maternal mutation is a one base pair insertion (3511insA) in the 3' terminal exon of LAMC2 resulting in a frameshift and a premature termination codon. Mutation 3511insA is predicted to lead to the synthesis of a gamma2 polypeptide (gamma2t) disrupted in its alpha-helical C-terminal structure and truncated of the last 25 amino acids. Keratinocytes isolated from the patient's skin showed a markedly decreased level of gamma2 chain mRNA and secreted scant amounts of laminin-5, which undergoes physiologic proteolytic processing. To investigate the biologic function of the laminin-5 molecules synthesized by the patient, mutant gamma2 cDNAs were transiently expressed in gamma2-null keratinocytes. Transfection of the gamma2Delta4 cDNA resulted in restoration of laminin-5 deposition onto the culture substrate, which demonstrates that the gamma2 polypeptides carrying a deletion in domain V, upstream of the gamma2 proteolytic cleavage site, are assembled into native laminin-5 that is secreted and extracellularly processed. In contrast, transfection of a mutant cDNA expressing the gamma2t chain failed to restore laminin-5 immunoreactivity, which indicates that integrity of the gamma2 C-terminal amino acid sequences is required for laminin-5 assembly. These results correlate for the first time a functional alteration in a laminin-5 domain with a mild junctional epidermolysis bullosa phenotype.

Amino Acid Sequence↗

PubMed2000

Pharmacologic treatment can prevent pancreatic injury after ERCP: a meta-analysis.

BACKGROUND: The identification of therapeutic agents that can prevent the pancreatic injury after endoscopic retrograde cholangiopancreatography (ERCP) is of considerable importance. METHODS: We performed a meta-analysis including 28 clinical trials on the use of somatostatin (12 studies), octreotide (10 studies), and gabexate mesilate (6 studies) after ERCP. Outcome measures evaluated were the incidence of acute pancreatitis, hyperamylasemia, and pancreatic pain. Three analyses were run separately: for all available studies, for randomized trials only, and for only those studies published as complete reports. RESULTS: When all available studies were analyzed, somatostatin and gabexate mesilate were significantly associated with improvements in all three outcomes. Odds ratios (OR) for gabexate mesilate were 0.27 (95% CI [0.13, 0. 57], p = 0.001) for acute pancreatitis, 0.66 (95% CI [0.48, -0.89], p = 0.007) for hyperamylasemia, and 0.33 (95% CI [0.18, 0.58], p = 0. 0005) for post-procedural pain. Somatostatin reduced acute pancreatitis (OR 0.38: 95% CI [0.22, 0.65], p < 0.001), pain (OR 0. 24: 95% CI [0.14, 0.42], p < 0.001), and hyperamylasemia (OR 0.65: 95% CI [0.48, 0.90], p = 0.008). Octreotide was associated only with a reduced risk of post-ERCP hyperamylasemia (OR 0.51: 95% CI [0.31, 0.83], p = 0.007) but had no effect on acute pancreatitis and pain. The statistical significance of data did not change after analyzing randomized trials only or studies published as complete reports. For each considered outcome, the publication bias assessment and the number of patients that need to be treated to prevent one adverse effect were, respectively, higher and lower for somatostatin than for gabexate mesilate. CONCLUSIONS: The pancreatic injury after ERCP can be prevented with the administration of either somatostatin or gabexate mesilate, but the former agent is more cost-effective. Additional studies comparing the efficacy of short-term infusion of somatostatin versus gabexate mesilate in patients at high risk for post-ERCP complications seem warranted.

Acute Disease↗

PubMed1997

Prolonged treatment (2 years) with different doses (3 versus 6 MU) of interferon alpha-2b for chronic hepatitis type C. Results of a multicenter randomized trial.

BACKGROUND/AIMS: To examine the effect of prolonged treatment with different doses of interferon alpha-2b on the relapse rate in patients with chronic hepatitis C. METHODS: One hundred and seventy-one patients with non-cirrhotic chronic hepatitis C were enrolled in an Italian multicenter trial. All patients were treated for 3 months with 3,000,000 Units (3 MU) of interferon alpha-2b given subcutaneously three times a week (t.i.w.). Patients with abnormal alanine aminotransferase (ALT) values were given 6 MU of interferon for an additional 3 months. If ALT remained persistently abnormal, therapy was then suspended. If ALT levels were normal, therapy was continued (6 MU t.i.w.) for an additional 18 months (total=2 years). Patients with normal ALT were randomly assigned to two groups, one receiving 3 MU and the other receiving 6 MU t.i.w. for an additional 21 months (total=2 years). Follow-up continued for 2 years after therapy withdrawal. RESULTS: Seven patients stopped treatment during the first 3 months. Of the remaining 164 patients, 76 (46%) showed abnormal ALT levels after 3 months of therapy: 11 of these (14%) normalized ALT values when given 6 MU and a sustained response was maintained in eight during the follow-up. Overall, 54 and 34 patients were allocated respectively to the groups receiving the 3 MU and 6 MU long-term treatment. At the end of therapy, 35/54 patients of the group 3 MU and 21/34 patients of the group 6 MU showed normal ALT levels (65% vs 62%, p=N.S.). After 2 years of follow-up, 24/35 (69%) patients of the group 3 MU and 16/21 (76%) of the group 6 MU were still in remission (p=N.S.). In an intention-to-treat analysis, 48/171 (28%) patients showed a long-term response (normal ALT values, HCV-RNA negative). About 65% of the sustained responders showed low baseline viremia compared with 33% of non-responders (p=0.005) while genotype 1b was more frequently found among non-responders than in long-term responders (84% vs 25%, p=0.0001). CONCLUSIONS: About 14% of patients who do not respond to a 3-month course of 3 MU of interferon normalize ALT levels when given 6 MU. In prolonged treatment, there is no significant difference between 3 and 6 MU in inducing a sustained response. Patients with low baseline viremia and genotype 2a respond significantly better to prolonged interferon therapy than highly viremic patients with genotype 1b.

Antiviral Agents↗

PubMed1997

HCV genotypes in patients with liver disease of different stages and severity.

UNLABELLED: AIMS/MATERIAL: Hepatitis C virus (HCV) genotyping was performed in 213 anti-HCV-positive patients with chronic liver disease ranging from minimal histological changes to hepatocellular carcinoma. One hundred and twenty-two patients had non-cirrhotic chronic active or persistent hepatitis (including 29 who were asymptomatic with persistently normal ALT levels) (chronic liver disease group). The other 91 had hepatocellular carcinoma and, in all but three cases, cirrhosis (hepatocellular carcinoma group). RESULTS: The overall prevalence of HCV variants was: 54.9% type 1b, 37.8% type 2, 2.5% type 1a, 2.0% type 3a, 2.0% type 4a. The genotype distribution showed no relation to the stage (chronic liver disease vs. hepatocellular carcinoma) or severity (chronic active vs. chronic persistent hepatitis) of the liver disease, or to the duration of the disease (<10 years vs. >10 years). Within the hepatocellular carcinoma group, the duration of type-1b disease was similar to that of type-2 infections. Ages at the time of infection and genotype were both independently associated with progression to cirrhosis and hepatocellular carcinoma, but multivariate analysis revealed that the effect of age was much stronger than that of genotype 1b. CONCLUSIONS: The predominance of HCV type 1b in this study reflects the higher frequency of this variant in our area. Our findings indicate that infections caused by each HCV genotype are capable of progressing to hepatocellular carcinoma.

Adolescent↗

PubMed1996

Hyper-negative template DNA supercoiling during transcription of the tetracycline-resistance gene in topA mutants is largely constrained in vivo.

The excess linking deficit of plasmid DNA from topoisomerase I-defective bacteria (topA mutants) results mainly from transcription and is commonly ascribed to unbalanced relaxation of transcription-induced twin-supercoiled domains. This defect is aggravated in genes for membrane-binding proteins (such as the tet gene) where anchoring of the transcription complex to the bacterial membrane is thought to enhance twin-domain partitioning. Thus, it is often assumed that the 'hyper-negative' linking difference of plasmid DNA from topA mutants reflects unconstrained, hyper-negative DNA supercoiling inside the cell. We tested the validity of this assumption in the present study. A DNA sequence that undergoes a gradual B to Z transition under increasing negative superhelical tension was used as a sensor of unconstrained negative supercoiling. Z-DNA formation was probed at a site upstream from the inducible pTac promoter fused either to the tet gene or to the gene for cytosolic chloramphenicol acetyl transferase (cat). Although plasmid DNA linking deficit increased more extensively in topA mutants following tet activation than following cat activation, no significant differences were observed in the extents to which the B to Z DNA transition is stimulated in the two cases. We infer that the excess linking deficit of the tet-containing plasmid DNA reflects constrained negative DNA supercoiling inside the cell.

Chloramphenicol O-Acetyltransferase↗

PubMed1996

A class of gyrase mutants of Salmonella typhimurium show quinolone-like lethality and require rec functions for viability.

We have identified a new class of DNA gyrase mutants of Salmonella typhimurium that show chronic derepression of the SOS regulon. Thus, these mutants mimic the response of wild-type cells to gyrase inhibitors of the quinolone family. SOS induction by conditional lethal mutations gyrA208 or gyrB652, like that mediated by quinolones, is completely dependent on the function of the recB gene product. Introduction of recA or recB null mutations into these strains exacerbates their temperature-sensitive phenotype and prevents growth at the otherwise permissive temperature of 37 degrees C. Selection of suppressors that concomitantly restore growth at 37 degrees C and SOS induction in a recB- background yielded mutations that relleve the RecB requirement for homologous recombination; namely, sbcB mutations as well as mutations at a new locus that was named sbcE. Such mutations also restore SOS induction in quinolone-treated gyr+ recB- strains. These findings indicate that Rec functions are needed for growth of the gyrase mutants at 37 degrees C and suggest that recombinational repair intermediates constitute the SOS-inducing signal in the mutants as well as in quinolone-treated wild-type bacteria. Unlike quinolones, however, the gyr mutations described in this study do not cause detectable accumulation of "cleavable' gyrase-DNA complexes in plasmid or chromosomal DNA. Yet gyrA208 (the only allele tested) was found to trigger RecB-mediated reckless degradation of chromosomal DNA in recA-cells at restrictive temperatures. Indirect evidence suggests that double-stranded DNA ends, entry sites for the RecBCD enzyme, are generated in the gyr mutants by the breakage of DNA-replication forks. We discuss how this could occur and how recombinational rescue of collapsed replication forks could account for cell survival (and SOS induction) in the gyr mutants as well as in quinolone-treated bacteria.

4-Quinolones↗

PubMed1996

Long-distance effect of downstream transcription on activity of the supercoiling-sensitive leu-500 promoter in a topA mutant of Salmonella typhimurium.

Expression of the lacZ gene from the supercoiling-sensitive leu-500 promoter on a plasmid in topA mutant cells was stimulated by activating a divergently oriented Tac promoter, 400 bp upstream from leu-500. The stimulation was approximately threefold regardless of whether the Tac promoter drove the expression of the tet gene, whose product is membrane bound, or of the cat gene, whose product is cytosolic. Putting a second copy of the Tac promoter downstream from lacZ, approximately 3,000 bp from leu-500 in the same orientation as the latter, resulted in 30-fold increase in lacZ expression upon isopropyl-beta-D-thiogalactopyranoside induction. Again, these effects were independent of the nature of the gene upstream from leu-500 (tet or cat). With both tet- and cat-harboring constructs, activation of the two Tac promoter copies caused plasmid DNA to become hypernegatively supercoiled in topA mutant cells. Thus, neither leu-500 activation nor hypernegative plasmid DNA supercoiling appears to require membrane anchoring of DNA in this system. Replacing the downstream copy of Tac with a constitutive promoter resulted in high-level lacZ expression even when the upstream copy was repressed. Under these conditions, no hypernegative DNA supercoiling was observed, indicating that the activity of plasmid-borne leu-500 in topA mutant cells does not necessarily correlate with the linking deficit of plasmid DNA. The response of the leu-500-lacZ fusion to downstream transcription provides a sensitive assay for transcriptional supercoiling in bacteria.

DNA Topoisomerases, Type I↗

PubMed1995

RNA polymerase (rpoB) mutants selected for increased resistance to gyrase inhibitors in Salmonella typhimurium.

Some rifampicin-resistance (RifR) mutations make bacteria slightly resistant to the gyrase inhibitors novobiocin (Nov) and nalidixic acid (Nal). This suggested that it might be possible to isolate rpoB mutants using either drug for positive selection. In an initial test, we confirmed the presence of Rif-resistant isolates among clones selected for Nov resistance. These mutants are also more resistant to Nal. In a subsequent experiment, we found that mutants selected for low-level resistance to Nal include isolates harboring mutations genetically linked to the rpoB locus; of two such mutants studied, one is temperature-sensitive for growth. These two mutants, which are only marginally affected in their response to Nov, are normally sensitive to Rif and thus might be representative of a new class of rpoB alleles. The Rif-resistant and Rif-sensitive rpoB alleles that increase resistance to gyrase inhibitors have one property in common: they all suppress, to varying degrees, the defect in his operon regulation (transcriptional deattenuation) caused by a gyrase defect or inhibition by novobiocin. To further analyse the transcription-supercoiling relationships in these mutants, we examined the ability of RNA polymerase to recruit gyrase activity during transcription. This was done by two independent approaches: (i) observing transcription-induced accumulation of hyper-negatively supercoiled plasmid DNA in a topA mutant background and (ii) measuring transcription-induced plasmid DNA cleavage in the presence of oxolinic acid. Results indicate that the rpoB alleles described in this study diminish the recruitment of gyrase activity by the transcription process. This property correlates with a decrease in the rate of transcription initiation.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA Gyrase↗

PubMed1994

The relative contributions of transcription and translation to plasmid DNA supercoiling in Salmonella typhimurium.

Mutations affecting DNA topoisomerase I (topA) in Salmonella typhimurium were isolated and graded on the basis of their ability to reverse the effects of gyrB mutations on his operon expression. Different topA and gyrB alleles (in otherwise isogenic strains) were used to gather insights into the transcription-dependent variability of plasmid DNA-linking deficit in growing bacteria. This study showed that modulation of DNA supercoiling by transcription results from the action of two components: one is highly dependent on the coupling of translation to RNA-chain elongation; and the other is unrelated to protein synthesis and entirely dependent on promoter determinants. The former greatly predominates in DNA topoisomerase I mutants (topA and topA gyrB) while the latter is the sole contributor to plasmid DNA-linking deficit in wild-type cells. Altogether, these data suggest that whereas translation acts by enhancing the formation of twin supercoiled domains during elongation, the promoter-dependent effects bear no relation to the twin-supercoiled-domain model and are better explained by a mechanism which responds to the binding/unwinding of template DNA by RNA polymerase.

Alleles↗

PubMed1993

The establishment of underdominant chromosomal rearrangements in multi-deme systems with local extinction and colonization.

The fate of an underdominant chromosomal mutant was investigated in multideme models with high rates of local extinction and colonization. Four models with different patterns of colonization (number of colonists and place of origin of colonists) were studied by performing a large number of computer simulations with the Monte Carlo method for several sets of values of the following parameters: coefficient of selection against the heterozygote, extinction rate of each deme, deme size, and number of demes. The probability of the newly arisen rearrangement being established in the multi-deme system depends strongly on the pattern of colonization, other things being equal. In the three models in which there is absent or scarce mixing of gene pools of different demes when a new deme is founded, the fixation probability of the new chromosomal rearrangement is rather close to that calculated by R. Lande (1979, Evolution 33, 234-251; 1985, Heredity 54, 323-332), which is equal to the corresponding probability in a single deme divided by the number of demes. In the model with extensive mixing of gene pools of demes, the corresponding probability is lower (considerably in some cases). Furthermore, in the models where the fixation probability is higher, the analysis of the time of the process leads to the conclusion that in systems consisting of a large number of demes, overlapping of several different processes of fixation of chromosomal rearrangements occurs.

Animals↗