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A Fels

Publications and source records attributed to A Fels.

At least 19 recordsLinked to original sources
PubMed2001

Transcription of potato spindle tuber viroid by RNA polymerase II starts predominantly at two specific sites.

Pospiviroidae, with their main representative potato spindle tuber viroid (PSTVd), are replicated via a rolling circle mechanism by the host-encoded DNA-dependent RNA polymerase II (pol II). In the first step, the (+)-strand circular viroid is transcribed into a (-)-strand oligomer intermediate. As yet it is not known whether transcription is initiated by promotors at specific start sites or is distributed non-specifically over the whole circle. An in vitro transcription extract was prepared from a non-infected potato cell culture which exhibited transcriptional activity using added circular PSTVd (+)-strand RNA as template. In accordance with pol II activity, transcription could be inhibited by alpha-amanitin. RT-PCR revealed the existence of at least two different start sites and primer extension identified these as nucleotides A(111) and A(325). The sequences of the first 7 nt transcribed are very similar, (105)GGAGCGA(111) and (319)GGGGCGA(325). GC-boxes are located at a distance of 15 and 16 nt upstream, respectively, in the native viroid structure, which may act to facilitate initiation. The GC-boxes may have a similar function to the GC-rich hairpin II in the (-)-strand intermediate, as described previously. The results are compared with the corresponding features of avocado sunblotch viroid, which belongs to a different family of viroids and exhibits different transcription initiation properties.

Base Sequence↗
PubMed1996

RNA structural features responsible for potato spindle tuber viroid pathogenicity.

The native structure of potato spindle tuber viroid (PSTVd) contains a series of short double helices and small internal loops that are organized into five structural domains. Nucleotides within the pathogenicity domain are known to play a critical role in modulating PSTVd symptom expression, and it has been suggested that disruption of a comparatively unstable "premelting region" within the pathogenicity domain may be required for disease induction. We have used a combination of quantitative bioassays, temperature gradient gel electrophoresis of circularized RNA transcripts, and thermodynamic calculations to compare the biological and structural properties of 12 representative PSTVd sequence variants. Certain mutations appeared to act indirectly, downregulating pathogenicity by suppressing the rate of PSTVd replication/accumulation. The effects of other mutations appeared to be more direct, but there was no consistent correlation between symptom severity and melting temperature. Taking into account the three-dimensional shape of RNA helices, comparison of the optimal secondary structures for these variants point to major differences in the geometry of their pathogenicity domains; i.e., variants producing intermediate symptoms possess a linear arrangement of three consecutive helices, whereas for variants producing mild or severe symptoms this domain is bent in opposing directions. Such alterations in RNA structure together with concomitant alterations in RNA-protein interaction(s) may be the primary cause of viroid pathogenicity.

Base Sequence↗
PubMed1995

Interdependence of pathogenicity and replicability with potato spindle tuber viroid.

After the unexpected appearance of lethal symptoms on tomato plants infected with the PSTVd strain Intermediate Di, viroids were isolated and sequenced. It was found that a new strain, named RG 1, had been generated spontaneously in our greenhouse. In a different series of plant passages two new strains, named QF A and QF B, were detected which coexisted with the wild-type strain Di. Strains QF A and QF B showed intermediate symptoms when inoculated separately. In order to confirm the working hypothesis that the more pathogenic strain outcompetes the less pathogenic strain but strains of similar pathogenicity might coexist in the host, strains of different pathogenicity were mixed for inoculation in a ratio from 1:1 to 1:100 (more pathogenic:less pathogenic). The concentrations of the individual strains were determined 6 weeks postinfection with the method of nondenaturing polyacrylamide gel electrophoresis, and the working hypothesis was confirmed. The total concentrations of viroids in infected plants were very similar, irrespective of whether severe, intermediate, or mild strains or mixtures of different strains were present. The mutations in all new strains (3 in RG 1, 2 in QF A, 3 in QF B) were located in the so-called virulence-modulating region. The mutations of strain RG 1 influenced dramatically the thermodynamic stability of the native rod-like structure, as determined experimentally by temperature-gradient gel electrophoresis. Since during replication a multihairpin structure is generated transiently which is transformed afterwards into the rod-like structure, a lower thermodynamic stability of the rod-like structure leads to a higher accumulation of the transient structure. It is assumed that the transient structure, which is active in replication as shown earlier, is essential also in pathogenesis. This model explains the experimentally determined interdependence between pathogenicity and replicability of PSTVd strains.

Base Sequence↗
PubMed1988

Cytomegalovirus pneumonia after bone marrow transplantation successfully treated with the combination of ganciclovir and high-dose intravenous immune globulin.

STUDY OBJECTIVE: To assess the efficacy of the combination of the antiviral agent ganciclovir (9-1,3 dihydroxy-2-propoxymethylguanine) and high-dose intravenous immune globulin for treating cytomegalovirus interstitial pneumonitis after allogeneic bone marrow transplantation. DESIGN: Nonrandomized prospective trial of combined treatment with two drugs; findings in these patients were compared with those in control patients treated with either of the two drugs alone. SETTING: Medical, pediatric, and intensive care units of a tertiary-care cancer treatment center. PATIENTS: Consecutive cases of 10 patients in the study group and of 11 patients in a historical control group with evidence of cytomegalovirus pneumonia after bone marrow transplantation for treatment of leukemia or congenital immune deficiency. INTERVENTIONS: Study Group (10 patients): ganciclovir, 2.5 mg/kg body weight, three times daily for 20 days, plus intravenous immune globulin, 500 mg/kg every other day for ten doses. Patients were then given ganciclovir, 5 mg/kg.d three to five times a week for 20 more doses, and intravenous immune globulin, 500 mg/kg twice a week for 8 more doses. Control Group (11 patients): ganciclovir alone (2 patients), 5 mg/kg twice a day for 14 to 21 days; cytomegalovirus hyperimmune globulin (5 patients), 400 mg/kg.d for 10 days; and intravenous immune globulin (4 patients), 400 mg/kg.d for 10 days. MEASUREMENTS AND MAIN RESULTS: Responses were observed in all patients treated with combination therapy; 7 of 10 patients were alive and well, and had no recurrence of disease at a median of 10 months after therapy. No therapeutic benefit was observed, and none of the 11 patients treated with either ganciclovir or intravenous immune globulin alone survived (P = 0.001 by Fisher exact test). CONCLUSIONS: Ganciclovir, when combined with high-dose intravenous immune globulin, appears to have significantly altered the outcome of patients with cytomegalovirus pneumonia after allogeneic bone marrow transplantation.

Acyclovir↗
PubMed1984

Abnormal B.A.E.P. in a family with Moebius syndrome: evidence for supranuclear lesion.

A family with Moebius syndrome is presented. Neurological lesions in the affected members are various: complete VI and VII cranial nerves palsy associated with mental retardation in the proband; left convergent strabismus and mental retardation in a brother of the proband and only mental retardation in a sister of the proband. The brainstem auditory evoked potentials (B.A.E.P.), investigated in the proband and his affected sister, are abnormal. The presence of the anomaly after the 3rd wave is consistent with a disfunction of the auditory tract at a supranuclear level. The mental deficiency and the supranuclear site of the acoustic lesion are an indication for a more general involvement of C.N.S. than cranial nerve nuclei alone. Karyotype and dermatoglyphics of the three affected subjects were normal. The authors hypothesized the same disorganogenetic factor acting very early (4th-6th week of gestational age) on the metamerization process of limb buds mesoderm and brainstem gray matter.

Abducens Nerve↗
PubMed1984

Friedreich's ataxia: clinical involvement and evoked potentials.

In 15 patients definitely affected by Friedreich's ataxia, precocious SEP abnormalities were constantly recorded independent of the duration of symptoms and the severity of clinical involvement; VEPs were frequently involved, but neither VEP abnormalities, nor visual impairment could be correlated with the severity or duration of Friedreich's ataxia clinical involvement; BAEPs were, to different extents, abnormal. These were completely dissociated from hearing disorders and significantly correlated (P less than 0.001) with Friedreich's ataxia clinical disability. Our observation of increased latency of the VEP P100 component and the early disappearance of BAEP Wave V with persistence of Wave I is in contrast with the hypothesis that changes are related to primary axonal degeneration. For practical purposes SEPs could help in the early diagnosis of Friedreich's ataxia, and BAEPs could be used for the electrophysiological monitoring of its clinical progression.

Adolescent↗