PubMed Health⌕ Search

Biomedical subjects

F Walter

Publications and source records attributed to F Walter.

At least 37 records · Page 2Linked to original sources
PubMed1999

Radiotherapy for stages I and IIA/B testicular seminoma.

Radiotherapy is generally accepted as a standard treatment for early-stage testicular seminoma. Relapse rates of 2% to 5% in clinical stage I and 10% to 20% in stage IIA/B (according to the Royal Marsden classification) can be achieved. Disease-specific survival reaches 100%. With such excellent cure rates, treatment-related side effects gain particular importance. Therefore, a prospective multicenter trial was initiated for radiotherapy of testicular seminoma with limited treatment portals and low total doses of irradiation. In clinical stage I, 483 patients were treated with 26 Gy to the para-aortic region only. In stage IIA, 42 patients and, in stage IIB, 18 patients received irradiation to the para-aortic and high iliac lymph nodes with 30 and 36 Gy, respectively. With a median time to follow-up of 55 months for stage I and 55.5 months for stage IIA/B, there were 18 (3.7%) and 4 (6.7%) cases of relapse in both treatment groups. Disease-specific survival was 99.6% in stage I and 100% in stage IIA/B. Acute toxicity was dominated by moderate gastro-intestinal side effects. No major late toxicity has been observed to date. Limited volume pure para-aortic treatment for stage I and para-aortic/high iliac irradiation for stage IIA/B with 26, 30 and 36 Gy, respectively, yields excellent cure rates with only moderate acute toxicity and is therefore recommended as standard treatment.

Adolescent↗
PubMed1999

Decay of the GRB 990123 optical afterglow: implications for the fireball model

Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer.

Journal Article↗
PubMed1999

Aminoglycoside-RNA interactions.

The structural and physico-chemical parameters promoting the binding of aminoglycosides to RNAs are becoming clear. The strength of the interaction is dominated by electrostatics, with the positively charged aminoglycosides displacing metal ions. Although aminoglycosides inhibit most known ribozymes, aminoglycosides or polyamines are able to catalyze specific RNA cleavage in the absence of metal ions.

Aminoglycosides↗
PubMed1998

Folding of the four-way RNA junction of the hairpin ribozyme.

The hairpin ribozyme consists of two loop-carrying duplexes (called A and B) that are adjacent arms of a four-way junction in its natural context in the viral RNA. We have shown previously that the activity of the ribozyme is strongly influenced by the structure adopted by the junction. In this study, we have used fluorescence resonance energy transfer to analyze the conformation and folding of the isolated four-way junction. Like other four-way RNA junctions, in the absence of added metal ions this junction adopts a square configuration of coaxially stacked arms, based on A on D and B on C stacking. Upon addition of magnesium ions, the junction undergoes an ion-induced transition to an antiparallel conformation. The data are consistent with folding induced by the binding of a single ion, with an apparent association constant in the range of 2000 M-1. Other divalent metal ions (calcium or manganese) can also induce this change in structure; however, sodium ions are unable to substitute for these ions, and are slightly inhibitory with respect to the transition. The loop-free hairpin junction adopts the same stacking conformer as the full ribozyme, but forms a more symmetrical X-shaped structure. In addition, the apparent stoichiometry of structural ion binding is lower for the isolated junction, and the affinity is considerably lower.

Calcium↗
PubMed1998

Structure and activity of the hairpin ribozyme in its natural junction conformation: effect of metal ions.

The natural form of the hairpin ribozyme consists of a four-way RNA junction of which the single-stranded loop-carrying helices are adjacent arms. The junction can be regarded as providing a framework for constructing the active ribozyme, and the rate of cleavage can be modulated by changing the conformation of the junction. We find that the junction-based form of the hairpin ribozyme is active in magnesium, calcium, or strontium ions, but not in manganese, cadmium, or sodium ions. Using fluorescence resonance energy transfer experiments, we have investigated the global structure of the ribozyme. The basic folding of the construct is based on pairwise helical stacking, so that the two loop-carrying arms are located on opposite stacked helical pairs. In the presence of magnesium, calcium, or strontium ions, the junction of the ribozyme undergoes a rotation into a distorted antiparallel geometry, creating close physical contact between the two loops. Manganese ions induce the same global folding, but no catalytic activity; this change in global conformation is therefore necessary but not sufficient for catalytic activity. Fitting the dependence of the conformation on ionic concentration to a two-state model suggests that cooperative binding of two ions is required to bring about the folding. However, further ion binding is required for cleavage activity. Cobalt hexammine ions also bring about global folding, while spermidine generates a more symmetrical form of the antiparallel structure. Cadmium ions generate a different folded form, interpreted in terms of close loop-loop association while the junction is unfolded. Sodium ions were unable to induce any folding of the ribozyme, which remained slightly parallel. These results are consistent with a folding process induced by the binding of two group IIA metal ions, distributed between the junction and the loop interface.

Base Sequence↗
PubMed1998

Folding of the hairpin ribozyme in its natural conformation achieves close physical proximity of the loops.

The hairpin ribozyme is a self-cleaving motif found in the negatives strand of the satellite RNA of some plant viruses. In its natural context, the ribozyme comprises four helices, two of which contain conserved formally unpaired loops, that are adjacent arms of a four-way RNA junction. We show that the arms that would carry these loops are brought close together in the global conformation of the isolated junction. Using fluorescence resonance energy transfer, we demonstrate a two-magnesium ion-dependent conformational transition of the complete ribozyme that brings the loopbearing arms into close physical proximity. The ribozyme is active as a four-way junction, and the rate of cleavage may be modulated by the conformation of the four-way junction.

Base Sequence↗
PubMed1998

Global structure of four-way RNA junctions studied using fluorescence resonance energy transfer.

Four-way helical junctions are found widely in natural RNA species. In this study, we have studied the conformation of two junctions by fluorescence resonance energy transfer. We show that the junctions are folded by pairwise coaxial helical stacking, forming one predominant stacking conformer in both examples studied. At low magnesium ion concentrations, the helical axes of both junctions are approximately perpendicular. One junction undergoes a rotation into a distorted antiparallel structure induced by the binding of a single magnesium ion. By contrast, the axes of the four-way junction of the U1 snRNA remain approximately perpendicular under all conditions examined, and we have determined the stacking conformer adopted.

Base Sequence↗
PubMed1998

[Comparative value of MR-angiography, helical CT and digital angiography in the preoperative assessment of abdominal aortic aneurysms].

PURPOSE: To compare helical CT with MR angiography in pre-operative assessment of abdominal aortic aneurysm (AAA). MATERIAL AND METHODS: Twenty patients with AAA underwent helical-CT, MR-angiography and digital angiography. All exams were interpreted independently by two groups of observers. Kappa and rho were calculated to assess correlations. Sensitivity and specificity were calculated to compare each method with the "gold standard" digital angiography. RESULTS: Inter-observer correlation was excellent. There was a very good agreement between both methods in the assessment of the maximal diameter and the proximal neck of the aneurysm. There was no significant difference in the assessment of stenoses of the visceral and iliac arteries, the number of renal arteries, and iliac extension. CONCLUSION: Helical CT and MR angiography are equivalent in pre-operative assessment of AAA.

Aged↗
PubMed1997

Ion-induced folding of the hammerhead ribozyme: a fluorescence resonance energy transfer study.

The ion-induced folding transitions of the hammerhead ribozyme have been analysed by fluorescence resonance energy transfer. The hammerhead ribozyme may be regarded as a special example of a three-way RNA junction, the global structure of which has been studied by comparing the distances (as energy transfer efficiencies) between the ends of pairs of labelled arms for the three possible end-to-end vectors as a function of magnesium ion concentration. The data support two sequential ion-dependent transitions, which can be interpreted in the light of the crystal structures of the hammerhead ribozyme. The first transition corresponds to the formation of a coaxial stacking between helices II and III; the data can be fully explained by a model in which the transition is induced by a single magnesium ion which binds with an apparent association constant of 8000-10 000 M-1. The second structural transition corresponds to the formation of the catalytic domain of the ribozyme, induced by a single magnesium ion with an apparent association constant of approximately 1100 M-1. The hammerhead ribozyme provides a well-defined example of ion-dependent folding in RNA.

Base Sequence↗
PubMed1997

Double-blind, randomized, placebo controlled study on the effects of the monophasic oral contraceptive containing 30 micrograms ethinyl estradiol and 2.00 mg dienogest on the hemostatic system.

Forty healthy female volunteers aged between 19 and 35 years (27.3 +/- 4.1 years) with normal menstrual cycles were included in a double-blind, randomized, placebo-controlled study to investigate the influence on the hemostatic system of an oral contraceptive containing 30 micrograms ethinyl estradiol in combination with 2.00 mg dienogest, which is a 19-norprogestin without a 17 alpha-ethinyl group. At baseline and during one treatment cycle, 12 hemostatic parameters were measured on cycle days 7, 14, and 21. The hemostatic parameters were categorized as either procoagulatory, anticoagulatory and profibrinolytic, or antifibrinolytic and indicative of fibrin turnover. Differences between placebo and 30 micrograms ethinyl estradiol and 2.00 mg dienogest of plasma levels of hemostatic parameters on cycle days 21 of the precycle and treatment cycle were chosen as target variables. Prothrombin fragment 1 + 2 (F 1 + 2) was chosen as the main target variable. Equivalence of F 1 + 2 between placebo and active treatment was noted. Among the procoagulatory factors, only factor VII activity was found to be increased over placebo in the active treatment group, but decreased in the placebo group. Protein C activity increased during the treatment with 30 micrograms ethinyl estradiol and 2.00 mg dienogest, and was higher than that of the placebo group in which this parameter decreased during the treatment cycle. There was a corresponding increase in fibrinolytic activity being reflected by higher plasminogen levels in the active treatment group in comparison with placebo. An increase was noted for the fibrinolytic parameter D-dimer. Apart from isolated measurements, the parameters remained in their respective normal ranges. The data combine to suggest that 30 micrograms ethinyl estradiol and 2.00 mg dienogest has a balanced effect on the hemostatic system stimulating both procoagulatory and fibrinolytic activity.

Adult↗
PubMed1997

Modulation of ovarian function by an oral contraceptive containing 30 micrograms ethinyl estradiol in combination with 2.00 mg dienogest.

Twenty-two healthy female volunteers with normal ovulatory cycles, aged between 20 and 34 years (27.3 +/- 4.1), were included in a single-center, noncomparative study to investigate the modulation of ovarian function by an oral contraceptive containing 30 micrograms ethinyl estradiol in combination with 2.00 mg dienogest. At baseline, during three treatment cycles and post-treatment, serum levels of luteinizing hormone, follicle-stimulating hormone, 17 beta-estradiol, and progesterone were assayed and ultrasonography was used to measure follicular size and the thickness of the endometrium. The primary efficacy variable was inhibition of ovulation as measured by ovarian activity grading. All volunteers ovulated during the pretreatment cycle. During treatment, none of the subjects had ovulatory cycles, although there was still some ovarian activity in several subjects. During the first treatment cycle, only 4% (1 subject) of cycles showed active follicle-like structures. The frequency of follicle-like structures increased to 33% and 35% during treatment cycles 2 and 3. The frequency of presumptive luteinized unruptured follicle-like structures was 5% (1 subject) and 15% (3 subjects) in treatment cycles 2 and 3. The serum hormone concentrations were effectively suppressed in comparison to baseline. The ovarian activity returned to baseline during the post-treatment period. One subject was excluded from further study because of a medical problem believed unrelated to use of the oral contraceptive. No serious adverse events were recorded during the course of the study. The results of the present investigation indicate that the modulatory effects on ovarian function of the monophasic oral-contraceptive containing 30 micrograms ethinyl estradiol combined with 2.00 mg dienogest lead to adequate suppression of ovarian activity and effective inhibition of ovulation.

Adult↗
PubMed1997

[Imaging of osteoarticular diseases of the anterior chest wall].

The purpose of this paper is to present a pictorial display of osseous and articular lesions of the anterior chest wall. The role of CT and MR imaging in such disorders is emphasized. Imaging of the anterior thoracic wall by plain films is particularly difficult. However numerous disorders may be encountered. They include inflammatory hyperostosis and sclerosis of the clavicle and the sternum, condensing osteitis and post-traumatic osteolysis of the clavicle, radiation osteitis of the sternum and the ribs, septic arthritis of the sternoclavicular joint, primary and secondary tumors of the sternum and the ribs. We illustrate a spectrum of such lesions in which CT and MR imaging provides acute evaluation of both soft tissue and bone details.

Clavicle↗
PubMed1995

Two inequivalent folding isomers of the three-way DNA junction with unpaired bases: sequence-dependence of the folded conformation.

The global structures of three-way helical junctions in DNA that contain two unpaired bases at the point of strand exchange have been studied. All such junctions examined undergo a folding in the presence of metal ions, to a structure in which there is coaxial stacking of two helices, with the third at an acute angle. However there are potentially two isomers of this structure possible, which are stereochemically inequivalent. We find that the majority of sequences studied by us fold into the isomer in which the polarity of the bulge-containing strand passing from the unstacked to the stacked helix is 5' to 3'. However, some sequences adopt the alternative stacking isomer, in which the polarity of the bulged strand is 3' to 5'. These isomeric differences are in complete agreement with the findings from two other studies by NMR. In addition to the isomeric differences, we find significant sequence-dependent differences within series of junctions that adopt the same isomeric form in the presence of ions. We conclude that the folding of bulged three-way DNA junctions is highly sequence-dependent.

Base Sequence↗
PubMed1992

Suppression of the growth and export defects of an Escherichia coli secA(Ts) mutant by a gene cloned from Bacillus subtilis.

A gene library of Bacillus subtilis chromosomal DNA was screened for genes capable of reverting the growth defects of the Escherichia coli secA51(Ts) mutant at 42 degrees C. A B. subtilis gene, designated csaA, was found to phenotypically suppress not only the growth defects of the E. coli mutant, but also to relieve the detrimental accumulation of precursors of exported proteins. The csaA gene encoded a protein of 15 kDa (137 amino acids) and was likely to be the distalmost member of an operon. No similarity to csaA was found among DNA or protein sequences deposited in databases. In contrast to other homologous or heterologous suppressors of the E. coli secA51(Ts) mutation, the csaA gene did not exert pleiotropic effects on either the E. coli secY24(Ts) or lep9(Ts) mutations. However, it restored the ability of a SecB-deficient mutant to grow on complex medium. It is proposed that CsaA serves as a molecular chaperone for exported proteins or alternatively acts by stabilizing the SecA protein.

Adenosine Triphosphatases↗