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G Stahl

Publications and source records attributed to G Stahl.

11 recordsLinked to original sources
PubMed2001

Programmed +1 frameshifting stimulated by complementarity between a downstream mRNA sequence and an error-correcting region of rRNA.

Like most retroviruses and retrotransposons, the retrotransposon Ty3 expresses its pol gene analog (POL3) as a translational fusion to the upstream gag analog (GAG3). The Gag3-Pol3 fusion occurs by frameshifting during translation of the mRNA that encodes the two separate but overlapping ORFs. We showed previously that the shift occurs by out-of-frame binding of a normal aminoacyl-tRNA in the ribosomal A site caused by an aberrant codonoanticodon interaction in the P site. This event is unlike all previously described programmed translational frameshifts because it does not require tRNA slippage between cognate or near-cognate codons in the mRNA. A sequence of 15 nt distal to the frameshift site stimulates frameshifting 7.5-fold. Here we show that the Ty3 stimulator acts as an unstructured region to stimulate frameshifting. Its function depends on strict spacing from the site of frameshifting. Finally, the stimulator increases frameshifting dependent on sense codon-induced pausing, but has no effect on frameshifting dependent on pauses induced by nonsense codons. Complementarity between the stimulator and a portion of the accuracy center of the ribosome, Helix 18, implies that the stimulator may directly disrupt error correction by the ribosome.

Amino Acid Sequence↗
PubMed2000

Nonsense-mediated decay mutants do not affect programmed -1 frameshifting.

Sequences in certain mRNAs program the ribosome to undergo a noncanonical translation event, translational frameshifting, translational hopping, or termination readthrough. These sequences are termed recoding sites, because they cause the ribosome to change temporarily its coding rules. Cis and trans-acting factors sensitively modulate the efficiency of recoding events. In an attempt to quantitate the effect of these factors we have developed a dual-reporter vector using the lacZ and luc genes to directly measure recoding efficiency. We were able to confirm the effect of several factors that modulate frameshift or readthrough efficiency at a variety of sites. Surprisingly, we were not able to confirm that the complex of factors termed the surveillance complex regulates translational frameshifting. This complex regulates degradation of nonsense codon-containing mRNAs and we confirm that it also affects the efficiency of nonsense suppression. Our data suggest that the surveillance complex is not a general regulator of translational accuracy, but that its role is closely tied to the translational termination and initiation processes.

Amino Acid Sequence↗
PubMed1999

Near-cognate peptidyl-tRNAs promote +1 programmed translational frameshifting in yeast.

Translational frameshifting is a ubiquitous, if rare, form of alternative decoding in which ribosomes spontaneously shift reading frames during translation elongation. In studying +1 frameshifting in Ty retrotransposons of the yeast S. cerevisiae, we previously showed that unusual P site tRNAs induce frameshifting. The frameshift-inducing tRNAs we show here are near-cognates for the P site codon. Their abnormal decoding induces frameshifting in either of two ways: weak codon-anticodon pairing allows the tRNA to disengage from the mRNA and slip +1, or an unusual codon-anticodon structure interferes with cognate in-frame decoding allowing out-of-frame decoding in the A site. We draw parallels between this mechanism and a proposed mechanism of frameshift suppression by mutant tRNAs.

Amino Acid Sequence↗
PubMed1997

In vivo HIV-1 frameshifting efficiency is directly related to the stability of the stem-loop stimulatory signal.

In many retroviruses, the expression of reverse transcriptase, protease, and integrase is dependent upon a -1 frameshift event. The frameshift signal is composed of a slippery sequence where the ribosome shifts, and a downstream stimulatory sequence. In most cases, the stimulatory sequence is a pseudoknot, but in some viruses, such as human immunodeficiency virus type 1 (HIV-1), a single stem-loop is involved. Here, we analyzed the precise role of the stem-loop thermodynamic stability. We tested the frameshifting stimulatory activity of a series of HIV-1-derived sequences showing a stepwise increment of the estimated deltaG degrees. These sequences were introduced at the junction of a lacZ-luc fusion gene cloned on a versatile expression vector, and the different constructs were tested in Saccharomyces cerevisiae and in mouse NIH3T3 cells. The results showed that the frameshifting efficiency was correlated directly to the stem stability between deltaG degrees = -2.5 kcal mol(-1) and deltaG degrees = -19.4 kcal mol(-1). This demonstrates the essential role of the stability of the stem-loop and does not support the involvement of a specific RNA-binding protein target sequence. However, increasing further the stem stability led to a diminution of frameshifting efficiency, suggesting that the stem-loop acts through a precise kinetic of pausing. Because the same pattern was observed in both yeast and mouse cells, it is likely that the stimulatory mechanism is conserved through evolution.

3T3 Cells↗
PubMed1995

Versatile vectors to study recoding: conservation of rules between yeast and mammalian cells.

In many viruses and transposons, expression of some genes requires alternative reading of the genetic code, also called recoding. Such events depend on specific mRNA sequences and can lead to read through of an in-frame stop codon or to +1 or -1 frameshifting. Here, we addressed the issue of conservation of recoding rules between the yeast Saccharomyces cerevisiae and mammalian cells by establishing a versatile vector that can be used to study recoding in both species. We first assessed this vector by analysing the site of +1 frameshift of the Ty1 transposon. Two sequences from higher organisms were then tested in both yeast and mammalian cells: the gag-pol junction of human immunodeficiency virus type 1 (HIV-1) (a site of -1 frameshift), and the stop codon region of the replicase cistron from the tobacco mosaic virus (a site of UAG read through). We show that both sequences direct a high level of recoding in yeast. Furthermore, different mutations of the target sequences have similar effects on recoding in yeast and in mouse cells. Most notably, a strong decrease of frameshifting was observed in the absence of the HIV-1 stem-loop stimulatory signal. Taken together, these data suggest that mechanisms of some recoding events are conserved between lower and higher eukaryotes, thus allowing the use of S. cerevisiae as a model system to study recoding on target sequences from higher organisms.

Animals↗
PubMed1988

Efficacy of a combination thromboxane receptor antagonist and lipoxygenase inhibitor in traumatic shock.

The effects of a thromboxane receptor antagonist having lipoxygenase inhibitory activity, L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) (1 mg/kg per h) were studied in a standardized model of traumatic shock. Pentobarbital (35 mg/kg) anesthetized rats subjected to Noble-Collip drum trauma were characterized by a 82 +/- 12 min survival time, a 20-fold increase in plasma cathepsin D activity, and a 6-fold increase in plasma myocardial depressant factor (MDF) activity. L-655,240 significantly attenuated the accumulation of MDF activity in the plasma (74 +/- 3 vs. 46 +/- 4 units/ml), vehicle vs. drug, respectively, and significantly (P less than 0.01) prolonged survival time to 206 +/- 26 min. However, plasma cathepsin D was not significantly altered with L-655,240 administration during traumatic shock. L-655,240 at 20 micrograms/ml markedly attenuated minced rat lung fragments from producing LTC4 and LTD4.L-655,240 exhibited significant anti-proteolytic activity in pancreatic homogenates. Therefore, L-655,2340 does not stabilize lysosomal membranes directly, but exerts an anti-proteolytic action which appears to curtail the production of a myocardial depressant factor by the ischemic pancreas, thus protecting during traumatic shock. A combination anti-eicosanoid drug such as L-655,240 may therefore prove to be an important therapeutic agent in acute ischemic disorders including traumatic shock.

Animals↗
PubMed1985

Relationship of prolonged pharmacologic serum levels of vitamin E to incidence of sepsis and necrotizing enterocolitis in infants with birth weight 1,500 grams or less.

The incidence of culture-proven neonatal sepsis and necrotizing enterocolitis (NEC) in preterm infants maintained at pharmacologic (mean 5.1 mg/dL +/- 1.45 SD) serum vitamin E levels for long periods was prospectively studied as part of a double-masked clinical trial of the effect of prophylactic vitamin E v placebo treatment on the development and course of retinopathy of prematurity (ROP). Within a few days of birth, 914 preterm infants were enrolled in the study; 545 (275 placebo-treated infants, 270 vitamin E-treated infants had birth weight of 1,500 g or less. A significant difference in incidence of neonatal sepsis (17 placebo-treated infants, 37 vitamin E-treated infants) and NEC (18 placebo-treated infants, 32 vitamin E-treated infants) was observed among infants who had been treated for eight or more days and who had developed neither sepsis nor NEC before that time. The association of vitamin E treatment with increased incidence of disease was much higher with sepsis than with NEC. The most likely reason for these observations is a pharmacologic serum vitamin E-related decrease in oxygen-dependent intracellular killing ability which results in a decreased resistance to infection in preterm infants. The data suggest that, if this occurs, it is clinically significant only in the more immature infants. In view of the known variability of absorption of oral vitamin E and the association between high serum vitamin E levels and increased incidence of sepsis and late-onset NEC reported here, it can be concluded that serum vitamin E levels must be monitored when supplemental vitamin E is administered to premature infants, especially those with birth weight 1,500 g or less. The risk-benefit ratio of long-term treatment using vitamin E at high serum levels should be clearly assessed.

Administration, Oral↗
PubMedDate not supplied

Pharmacology and biological efficacy of a recombinant, humanized, single-chain antibody C5 complement inhibitor in patients undergoing coronary artery bypass graft surgery with cardiopulmonary bypass.

BACKGROUND: Cardiopulmonary bypass (CPB) induces a systemic inflammatory response that causes substantial clinical morbidity. Activation of complement during CPB contributes significantly to this inflammatory process. We examined the capability of a novel therapeutic complement inhibitor to prevent pathological complement activation and tissue injury in patients undergoing CPB. METHODS AND RESULTS: A humanized, recombinant, single-chain antibody specific for human C5, h5G1.1-scFv, was intravenously administered in 1 of 4 doses ranging from 0.2 to 2.0 mg/kg before CPB. h5G1.1-scFv was found to be safe and well tolerated. Pharmacokinetic analysis revealed a sustained half-life from 7.0 to 14.5 hours. Pharmacodynamic analysis demonstrated significant dose-dependent inhibition of complement hemolytic activity for up to 14 hours at 2 mg/kg. The generation of proinflammatory complement byproducts (sC5b-9) was effectively inhibited in a dose-dependent fashion. Leukocyte activation, as measured by surface expression of CD11b, was reduced (P<0.05) in patients who received 1 and 2 mg/kg. There was a 40% reduction in myocardial injury (creatine kinase-MB release, P=0.05) in patients who received 2 mg/kg. Sequential Mini-Mental State Examinations (MMSE) demonstrated an 80% reduction in new cognitive deficits (P<0.05) in patients treated with 2 mg/kg. Finally, there was a 1-U reduction in postoperative blood loss (P<0. 05) in patients who received 1 or 2 mg/kg. CONCLUSIONS: A single-chain antibody specific for human C5 is a safe and effective inhibitor of pathological complement activation in patients undergoing CPB. In addition to significantly reducing sC5b-9 formation and leukocyte CD11b expression, C5 inhibition significantly attenuates postoperative myocardial injury, cognitive deficits, and blood loss. These data suggest that C5 inhibition may represent a novel therapeutic strategy for preventing complement-mediated inflammation and tissue injury.

Antibodies, Monoclonal↗