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Biomedical subjects

S Powers

Publications and source records attributed to S Powers.

At least 55 records · Page 3Linked to original sources
PubMed1991

Overexpression of RPI1, a novel inhibitor of the yeast Ras-cyclic AMP pathway, down-regulates normal but not mutationally activated ras function.

A high-copy-number plasmid genomic library was screened for genes that when overexpressed down-regulate Ras protein activity in Saccharomyces cerevisiae. We report on the structure and characterization of one such gene, RPI1, which potentially encodes a novel 46-kDa negative regulator of the Ras-cyclic AMP pathway. Three lines of evidence suggest that the RPI1 gene product operates upstream to negatively regulate the activity of normal but not mutationally activated Ras proteins: (i) overexpressed RPI1 lowers cyclic AMP levels in wild-type yeast cells but not in yeast cells carrying the RAS2Val-19 mutation, (ii) overexpressed RPI1 suppresses the heat shock sensitivity phenotype induced by overexpression of normal RAS2 but does not suppress the same phenotype induced by RAS2Val-19, and (iii) disruption of RPI1 results in a heat shock sensitivity phenotype which can be suppressed by mutations that lower normal Ras activity. Thus, RPI1 appears to encode an inhibitor of Ras activity that shares a common feature with Ras GTPase-activating proteins in that it fails to down-regulate activated RAS2Val-19 function. We present evidence that the down-regulatory effect of RPI1 requires the presence of one of the two Ras GTPase activators, IRA1 and IRA2.

Amino Acid Sequence↗
PubMed1991

Accuracy of pulse oximeters in estimating heart rate at rest and during exercise.

Pulse oximeters are being widely used for non-invasive, simultaneous assessment of haemoglobin oxygen saturation. They are reliable, accurate, relatively inexpensive and portable. Pulse oximeters are often used for estimating heart rate at rest and during exercise. However, at present the data available to validate their use as heart rate monitors are not sufficient. We evaluated the accuracy of two oximeters (Radiometer, ear and finger probe; Ohmeda 3700, ear probe) in monitoring heart rate during incremental exercise by comparing the pulse oximeters with simultaneous ECG readings. Data were collected on eight men (713 heart rate readings) during graded cycle ergometer and treadmill exercise to volitional fatigue. Analysis by linear regression revealed that general oximeter readings significantly correlated with those of ECG (r = 0.91, P less than 0.0001). However, comparison of heart rate at each level of work showed that oximeter readings significantly (P less than 0.05) under-estimated rates above 155 beats/min. These results indicate that the use of pulse oximeters as heart rate monitors during strenuous exercise is questionable. This inaccuracy may well originate from the instability of the probes, sweating, other artefacts during exercise, and measurement of different components in the cardiovascular cycle.

Adult↗
PubMed1990

Cloning and characterization of CAP, the S. cerevisiae gene encoding the 70 kd adenylyl cyclase-associated protein.

Adenylyl cyclase from S. cerevisiae contains at least two subunits, a 200 kd catalytic subunit and a subunit with an apparent molecular size of 70 kd, which we now call CAP (cyclase-associated protein). We cloned a cDNA encoding CAP by screening a yeast cDNA expression library in E. coli with antisera raised against the purified protein. The cDNA contained an open reading frame capable of encoding a 526 amino acid protein that is not homologous to any sequences in the current data bases. Adenylyl cyclase activity in membranes from cells that lacked CAP was not stimulated by RAS2 proteins in vitro. These results suggest that CAP is required for at least some aspects of the RAS-responsive signaling system. Mutants lacking CAP had four additional phenotypes that appear to be unrelated to effects of the RAS/adenylyl cyclase pathway: the inability to grow on rich medium (YPD), temperature sensitivity on minimal medium, sensitivity to nitrogen starvation, and a swollen cell morphology.

Adenylyl Cyclases↗
PubMed1990

Mutants of Saccharomyces cerevisiae defective in the farnesylation of Ras proteins.

Ras proteins are post-translationally modified by farnesylation. In the present investigation, we identified an activity in crude soluble extracts of yeast cells that catalyzes the transfer of a farnesyl moiety from farnesyl pyrophosphate to yeast RAS2 protein. RAS2 proteins having a C-terminal Cys-Ali-Ali-Xaa sequence (where Ali is an aliphatic amino acid and Xaa is the unspecified C-terminal amino acid) served as substrates for this reaction, whereas RAS2 proteins with an altered or deleted Cys-Ali-Ali-Xaa sequence did not. A yeast mutant, dpr1/ram1, originally isolated as a Ras-processing mutant was shown to be defective in farnesyltransferase activity. In addition, another mutant, ram2, also was defective in the transferase activity. These results demonstrate that at least two genes, DPR1/RAM1 and RAM2, are required for the farnesyltransferase activity in yeast.

Alkyl and Aryl Transferases↗
PubMed1990

Adaptation in adolescence: the influence of time and severe psychiatric disorder.

This study reports the development of adaptive processes in two groups of adolescents assessed initially and 2 years later with clinical research interviews. Students from a public high school (N = 44) and inpatients on an adolescent psychiatric ward (N = 51) formed the two subject groups. The psychiatrically hospitalized group had significantly improved scores after a 2-year interval on four of six adaptive process Summary Scales: Task Orientation, Relatedness, Self Knowledge, and Inner Synthetic Functions. However, these higher scores did not reach the levels of the high school group at either point of assessment. The scores in the high school group remained stable over time except for an increase in the area of Self Knowledge. The value of this interview-derived assessment, in comparison to other forms of measurement, is discussed, and consideration is given to factors which contribute to the differences between groups.

Adaptation, Psychological↗
PubMed1990

Ventilatory response of spinal cord-lesioned subjects to electrically induced exercise.

Seven human spinal cord-lesioned subjects (SPL) underwent electrically induced muscle contractions (EMC) of the quadriceps and hamstring muscles for 10 min: 5 min control, 2 min with venous return from the legs occluded, and 3 min postocclusion. Group mean changes in CO2 output compared with rest were +107 +/- 30.6, +21 +/- 25.7, and +192 +/- 37.0 (SE) ml/min during preocclusion, occlusion, and postocclusion EMC, respectively. Mean arterial CO2 partial pressure (PaCO2) obtained from catheterized radial arteries at 15- to 30-s intervals showed a significant (P less than 0.05) hypocapnia (36.2 Torr) during occlusion and a significant (P less than 0.05) hypercapnia (38.1 Torr) postocclusion relative to a group mean preocclusion EMC PaCO2 of 37.5 Torr. Relative to preocclusion EMC, expired ventilation (VE) decreased during occlusion and increased after release of occlusion. However, changes in VE always occurred after changes in end-tidal PCO2 (mean 41 s after occlusion and 10 s after release of occlusion). In the two subjects investigated during hyperoxia, the VE and PaCO2 responses to occlusion and release did not differ from normoxia. We conclude that the data do not support mediation of the EMC hyperpnea in SPL by humoral mechanisms that others have proposed for mediation of the exercise hyperpnea in spinal cord-intact humans.

Blood Pressure↗
PubMed1989

Dominant yeast and mammalian RAS mutants that interfere with the CDC25-dependent activation of wild-type RAS in Saccharomyces cerevisiae.

Two mutant alleles of RAS2 were discovered that dominantly interfere with wild-type RAS function in the yeast Saccharomyces cerevisiae. An amino acid substitution which caused the dominant interference was an alanine for glycine at position 22 or a proline for alanine at position 25. Analogous mutations in human H-ras also dominantly inhibited RAS function when expressed in yeast cells. The inhibitory effects of the mutant RAS2 or H-ras genes could be overcome by overexpression of CDC25, but only in the presence of wild-type RAS. These results suggest that these mutant RAS genes interfere with the normal interaction of RAS and CDC25 proteins and suggest that this interaction is direct and has evolutionarily conserved features.

Alleles↗
PubMed1988

A mutation in the catalytic subunit of cAMP-dependent protein kinase that disrupts regulation.

A mutant catalytic subunit of adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase has been isolated from Saccharomyces cerevisiae that is no longer subject to regulation yet retains its catalytic activity. Biochemical analysis of the mutant subunit indicates a 100-fold decreased affinity for the regulatory subunit. The mutant catalytic subunit exhibits approximately a threefold increase in Michaelis constant for adenosine triphosphate and peptide cosubstrates, and is essentially unchanged in its catalytic rate. The nucleotide sequence of the mutant gene contains a single nucleotide change resulting in a threonine-to-alanine substitution at amino acid 241. This residue is conserved in other serine-threonine protein kinases. These results identify this threonine as an important contact between catalytic and regulatory subunits but only a minor contact in substrate recognition.

Amino Acid Sequence↗
PubMed1988

Effects of beta-adrenergic blockade on ventilation and gas exchange during the rest to work transition.

The purpose of these experiments was to determine the effects of acute beta-blockade on the kinetics of oxygen uptake (VO2), expired carbon dioxide (VCO2), and expired ventilation (VE) in the transition from rest to submaximal exercise. Six male subjects exercised for 6 min on a cycle ergometer (60 W) initiated as a square wave from rest on two occasions. The beta-blockade experiment began 60 min after the subject ingested propranolol hydrochloride (1 mg.kg-1 BW) while the second experiment served as control with the treatment order counterbalanced. Ventilation and gas exchange were monitored by open circuit techniques and the data were modeled with a single-component exponential function using a time delay. No differences existed (p greater than 0.05) in the steady state VO2, VCO2, or VE nor the kinetics of VCO2 and VE between treatments. However, the rate of adaptation of VO2 toward steady state was significantly slowed (p less than 0.05) with beta-blockade. These data suggest that acute beta blockade results in diminished VO2 kinetics in the transition from rest to steady-state exercise. We hypothesize that the mechanism to explain this finding is a slowed time course of cardiac output adjustment at the beginning of exercise.

Adult↗
PubMed1988

Effects of beta-adrenergic blockade on ventilation and gas exchange during incremental exercise.

Controversy exists concerning the effects of acute beta-adrenergic blockade on ventilation during exercise. Hence, the purpose of this study was to determine the effects of acute beta blockade on ventilation and gas exchange during incremental exercise. Nine male subjects underwent incremental exercise on a cycle ergometer (30 W.min-1) to exhaustion, with one trial being performed 60 min after the subject ingested propranolol hydrochloride (Inderal 1 mg.kg-1 BW) while the second test served as control. The treatment order was counterbalanced to preclude any ordering effect on the results, and 1 week separated the tests. Ventilation and gas exchange were monitored by open circuit techniques. No difference (p greater than 0.05) existed in VE, % Hb sat, VCO2, ventilatory threshold, and VE/VCO2 between treatments at the same exercise stage. VO2max was lowered from 3.82 to 3.26 l.min-1 (p less than 0.05) and HRmax was reduced from 190 to 150 bpm (p less than 0.05) as a result of beta blockade. These data suggested that acute beta blockade had no effect on exercise ventilation, but decreased HRmax at comparable work rates. In addition, VO2max and exercise time to exhaustion were hindered, probably due to beta blockade limitation of HRmax, and, thus, oxygen transport.

Adult↗
PubMed1987

The S. cerevisiae CDC25 gene product regulates the RAS/adenylate cyclase pathway.

The gene corresponding to the S. cerevisiae cell division cycle mutant cdc25 has been cloned and sequenced, revealing an open reading frame encoding a protein of 1589 amino acids that contains no significant homologies with other known proteins. Cells lacking CDC25 have low levels of cyclic AMP and decreased levels of Mg2+-dependent adenylate cyclase activity. The lethality resulting from disruption of the CDC25 gene can be suppressed by the presence of the activated RAS2val19 gene, but not by high copy plasmids expressing a normal RAS2 or RAS1 gene. These results suggest that normal RAS is dependent on CDC25 function. Furthermore, mutationally activated alleles of CDC25 are capable of inducing a set of phenotypes similar to those observed in strains containing a genetically activated RAS/adenylate cyclase pathway, suggesting that CDC25 encodes a regulatory protein. We propose that CDC25 regulates adenylate cyclase by regulating the guanine nucleotide bound to RAS proteins.

Adenylyl Cyclases↗
PubMed1986

RAM, a gene of yeast required for a functional modification of RAS proteins and for production of mating pheromone a-factor.

We have identified a gene (SUPH) of S. cerevisiae that is required for both RAS function and mating by cells of a mating type. supH is allelic to ste16, a gene required for the production of the mating pheromone a-factor. Both RAS and a-factor coding sequences terminate with the potential acyltransferase recognition sequence Cys-A-A-X, where A is an aliphatic amino acid. Mutations in SUPH-STE16 prevent the membrane localization and maturation of RAS protein, as well as the fatty acid acylation of it and other membrane proteins. We propose the designation RAM (RAS protein and a-factor maturation function) for SUPH and STE16. RAM may encode an enzyme responsible for the modification and membrane localization of proteins with this C-terminal sequence.

Acylation↗
PubMed1986

Peak oxygen uptake in arm ergometry: effects of testing protocol.

The purpose of this investigation was to determine if a new proposed arm ergometer protocol was advantageous in eliciting higher peak oxygen uptake (peak VO2) when compared with two protocols currently referred to in the literature. Ten male subjects were tested on three different exercise protocols; a discontinuous test (DT), a continuous test (CT) and a new proposed jump-max test (JMT). The CT began at a work rate of 33 watts (W) (40 rpm) with the power output (PO) being increased 16 W every 3 minutes. The DT began without resistance on the ergometer flywheel (50 rpm) and the work rate was increased by 25 W every 3 minutes with a 1-minute rest between stages. The JMT began with a 3-minute pretest to determine a PO which elicited a HR of 120 +/- 5 beat min-1. After a 2-minute rest, subjects began exercise at the predetermined work rate (80 rpm) with the PO being increased 20 W each minute of the test. Oxygen uptake was measured minute by minute via open circuit spirometry. Peak VO2 was higher (p less than 0.05) in the JMT (mean +/- SEM = 2.36 +/- 0.06 l.min-1) when compared with either (means +/- SEM = 2.16 +/- 0.07 l.min-1) or the CT (means +/- SEM = 2.04 +/- 0.10 l.min-1). No difference (p greater than 0.05) existed in peak VO2 between the CT and the DT. These data suggest that the proposed JMT may result in a higher measured peak VO2 in subjects when compared with either DT or CT of moderate to long duration.

Adolescent↗
PubMed1986

Exploring the function of RAS oncogenes by studying the yeast Saccharomyces cerevisiae.

The RAS oncogenes comprise a family of genes found to be activated in perhaps 10-20% of human cancers and which have been highly conserved in evolution. Homologs of the mammalian RAS exist in the yeast Saccharomyces cerevisiae (RAS1 and RAS2). We have shown that human ras proteins can complement the loss of RAS1 and RAS2 proteins in yeast, and hence are functionally homologous. Both human and yeast RAS proteins can stimulate the magnesium and guanine nucleotide-dependent adenylate cyclase activity present in yeast membranes. However, RAS proteins do not appear to stimulate adenylate cyclase in vertebrate cells. Our studies indicate that although RAS proteins are essential controlling elements of adenylate cyclase in yeast, they have other essential functions in that organisms. RAS proteins are themselves probably controlled by growth regulatory proteins.

Fungal Proteins↗
PubMed1985

Functional homology of mammalian and yeast RAS genes.

Yeast spores lacking endogenous RAS genes will not germinate. If such spores contain chimeric mammalian/yeast RAS genes or even the mammalian H-ras gene under the control of the galactose-inducible GAL10 promoter, they will germinate in the presence of galactose and produce viable haploid progeny dependent on galactose for continued growth and viability. These results indicate that the biochemical function of RAS proteins is essential for vegetative haploid yeast and that this function has been conserved in evolution since the progenitors of yeast and mammals diverged.

Animals↗
PubMed1985

In yeast, RAS proteins are controlling elements of adenylate cyclase.

S. cerevisiae strains containing RAS2val19, a RAS2 gene with a missense mutation analogous to one that activates the transforming potential of mammalian ras genes, have growth and biochemical properties strikingly similar to yeast strains carrying IAC or bcy1. Yeast strains carrying the IAC mutation have elevated levels of adenylate cyclase activity. bcy1 is a mutation that suppresses the lethality in adenylate cyclase deficient yeast. Yeast strains deficient in RAS function exhibit properties similar to adenylate cyclase deficient yeast. bcy1 suppresses lethality in ras1- ras2- yeast. Compared to wild-type yeast strains, intracellular cyclic AMP levels are significantly elevated in RAS2val19 strains, significantly depressed in ras2- strains, and virtually undetectable in ras1- ras2- bcy1 strains. Membranes from ras1- ras2- bcy1 yeast lack the GTP-stimulated adenylate cyclase activity present in membranes from wild-type cells, and membranes from RAS2val19 yeast strains have elevated levels of an apparently GTP-independent adenylate cyclase activity. Mixing membranes from ras1- ras2- yeast with membranes from adenylate cyclase deficient yeast reconstitutes a GTP-dependent adenylate cyclase.

Adenylyl Cyclases↗