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Biomedical subjects

P F Miller

Publications and source records attributed to P F Miller.

36 records · Page 2Linked to original sources
PubMed1991

A quantitative model for translational control of the GCN4 gene of Saccharomyces cerevisiae.

Expression of the GCN4 gene of Saccharomyces cerevisiae is regulated at the translational level by short open reading frames (uORFs) present in the leader sequence of its mRNA. Under conditions of amino acid sufficiency, these sequences restrict the flow of initiating ribosomes to the GCN4 AUG start codon. Mutational analysis of GCN4 has led to a model in which ribosomes must translate the 5'-proximal uORF1 and reassemble an initiation complex in order to translate GCN4. This reassembly process is thought to be rapid when amino acids are abundant, such that reinitiation occurs at uORF2, uORF3, or uORF4. Reinitiation at these sites prevents translation of GCN4, presumably because ribosomes dissociate from the mRNA following termination at uORFs 2 to 4. Because of reduced initiation factor activity under starvation conditions, a substantial fraction of ribosomal subunits scanning downstream from uORF1 are not ready to reinitiate when they reach uORFs 2 to 4, but become competent to do so while scanning the additional sequences between uORF4 and GCN4. Examination of the effects of point mutations in the ATG codons of the different uORFs suggests a quantitative model for this control mechanism that describes the probability of reinitiation as a function of the distance scanned downstream from uORF1. This model accounts for the phenotypes of a number of deletion and insertion mutations that alter the intercistronic spacing between the uORFs and GCN4. The correspondence between observed and predicted results implies that the differential rates of reinitiation at GCN4 versus uORFs 2 to 4 are determined largely by the different scanning times required to reach each of these start sites following translation of uORF1. In addition, it supports the notion that an increased scanning-time requirement for reinitiation in amino acid-starved cells forms the basis for translational derepression of GCN4 expression.

Amino Acids↗
PubMed1990

cis-acting sequences involved in the translational control of GCN4 expression.

Four short upstream open reading frames (uORFs) in the mRNA leader are required for the translational control of GCN4 expression in response to amino acid availability. Data are reviewed demonstrating that the fourth (3' proximal) uORF is sufficient to establish the repressed levels of GCN4 expression, while the first uORF functions as a positive regulatory element under starvation conditions to stimulate GCN4 translation. Furthermore, positive and negative trans-acting regulatory factors, the activities of which appear to be modulated according to amino acid availability, exert their effects on GCN4 expression through the uORFs. Direct comparison of the uORFs indicates that there are important nucleotide sequence differences between uORF1 and 4, and that these are located primarily around the termination codons of these elements. Recent findings suggest that the sequences that mediate repression of GCN4 expression are complex, but can be overcome under starvation conditions by ribosomes that have previously translated uORF1.

Alleles↗
PubMed1990

Aging and pain perception in ischemic heart disease.

Age is a recognized risk factor for coronary artery disease, but the relationship between age and silent ischemia is not well understood. We analyzed the data from 35 rest/stress radionuclide ventriculography examinations in patients with documented ischemic coronary artery disease who had experienced 1 mm ST segment depression accompanied by angina during exercise testing. An index of ischemic cardiac pain perception (PPI) was calculated by subtracting the time of onset of 1 mm ST segment depression from the time of onset of angina. The mean value of PPI was -97 +/- 311 seconds. PPI was significantly correlated with age (r = 0.37, p = 0.03). This suggests that as age increases, perception of pain during myocardial ischemic episodes becomes muted. This relationship remained significant when we controlled for the presence of medication and severity of disease (change in ejection fraction from rest to peak exercise). These findings suggest that age is an independent risk factor for a decreased perception of ischemic cardiac pain, and thus for silent myocardial ischemia.

Adult↗
PubMed1990

Pharmacokinetics of prednisolone in children with nephrosis.

The pharmacokinetics of prednisolone given intravenously were studied in 11 children with relapsed steroid responsive nephrotic syndrome, and four control subjects. The clearance of both total and unbound drug was decreased in these children and the unbound fraction of the drug in plasma was significantly correlated with the degree of hypoalbuminaemia. We conclude that changes in the clearance of prednisolone and altered protein binding might account for some of the variability in both therapeutic responses and the incidence of toxicity in patients treated with standard dosage regimens.

Adolescent↗
PubMed1990

Human selenium status and glutathione peroxidase activity in north-west England.

Nutritional selenium deficiency disease, due to low soil selenium content, is well recognized in British livestock. The adequacy of the selenium status of 25 healthy human volunteers, 50 blood donors, 94 general medical patients and 106 allergy clinic patients was investigated in 1987/8 by measuring serum selenium concentration and platelet glutathione peroxidase activity. Mean serum selenium concentration for the entire study population was 92 micrograms/l. Significant linear correlations between serum selenium concentration and peroxidase activity indicate that a substantial proportion of both healthy volunteers and medical patients are of low selenium nutritional status. Twenty-five per cent of healthy volunteers and 50 per cent of medical patients had serum selenium values below those required for full expression of selenium-dependent enzyme activity. Deficiency of the antioxidant activities of selenium and selenium-dependent enzymes may be relevant to geographical differences in morbidity from a wide range of human disease states.

Administration, Oral↗
PubMed1989

Sequences that surround the stop codons of upstream open reading frames in GCN4 mRNA determine their distinct functions in translational control.

Translational control of the GCN4 gene of Saccharomyces cerevisiae requires at least two of the four short upstream open reading frames (URFs) in the leader of GCN4 mRNA. URF4 is a strong negative element that is sufficient for repression of GCN4 expression in normal growth conditions. URF1 is approximately 30-fold less effective as a translational barrier when it is the single URF present in the mRNA leader and is required upstream from URF4 for efficient derepression of GCN4 expression under amino acid starvation conditions. We show that the last codon plus 10 bp immediately after the stop codon of URF4 are sufficient to convert URF1 into a strong translational barrier when it is present as a solitary URF. This result suggests that the characteristics of translation termination at URF4 are responsible largely for its strong inhibitory effect on translation initiation at the GCN4 AUG codon. Introduction of the same URF4 sequences at URF1 also reduces GCN4 expression under derepressing conditions when URF1 is upstream from URF4. This fact suggests that URF1 translation normally is compatible with efficient scanning and initiation downstream and that this property is required for its ability to overcome the translational barrier at URF4. These findings are consistent with the idea that ribosomes must first translate URF1 and then resume scanning in order to traverse URF4 sequences under starvation conditions. Our results indicate that nucleotides located 3' to the stop codon can be as important as those located 5' to the start site in determining the inhibitory effect of an URF on translation initiation downstream.

Base Sequence↗
PubMed1988

The first and fourth upstream open reading frames in GCN4 mRNA have similar initiation efficiencies but respond differently in translational control to change in length and sequence.

The third and fourth AUG codons in GCN4 mRNA efficiently repress translation of the GCN4-coding sequences under normal growth conditions. The first AUG codon is approximately 30-fold less inhibitory and is required under amino acid starvation conditions to override the repressing effects of AUG codons 3 and 4. lacZ fusions constructed to functional, elongated versions of the first and fourth upstream open reading frames (URFs) were used to show that AUG codons 1 and 4 function similarly as efficient translational start sites in vivo, raising the possibility that steps following initiation distinguish the regulatory properties of URFs 1 and 4. In accord with this idea, we observed different consequences of changing the length and termination site of URF1 versus changing those of URFs 3 and 4. The latter were lengthened considerably, with little or no effect on regulation. In fact, the function of URFs 3 and 4 was partially reconstituted with a completely heterologous URF. By contrast, certain mutations that lengthen URF1 impaired its positive regulatory function nearly as much as removing its AUG codon did. The same mutations also made URF1 a much more inhibitory element when it was present alone in the mRNA leader. These results strongly suggest that URFs 1 and 4 both function in regulation as translated coding sequences. To account for the phenotypes of the URF1 mutations, we suggest the most ribosomes normally translate URF1 and that the mutations reduce the number of ribosomes that are able to complete URF1 translation and resume scanning downstream. This effect would impair URF1 positive regulatory function if ribosomes must first translate URF1 in order to overcome the strong translational block at the 3'-proximal URFs. Because URF1-lacZ fusions were translated at the same rate under repressing and derepressing conditions, it appears that modulating initiation at URF1 is not the means that is used to restrict the regulatory consequences of URF1 translation to starvation conditions.

Base Sequence↗
PubMed1987

The separation of unbound prednisolone in plasma by centrifugal ultrafiltration.

To study variable plasma protein binding of prednisolone in children with nephrotic syndrome we have devised a simple rapid method for measuring unbound prednisolone. The plasma was initially ultrafiltered at 37 degrees C fixed angle head at 1500 g for 30 min then the filtrate was analysed by high pressure liquid chromatography. The effects of variable ultrafiltration conditions were studied. The method was used to compare the AUC unbound prednisolone in a nephrotic child (plasma albumin concentration 18 g L-1) with a control (plasma albumin concentration 43 g L-1); their respective AUC unbound prednisolone values were 4.02 mg h L-1 and 1.07 mg h L-1.

Adult↗
PubMed1987

Emergency coronary angioplasty for acute myocardial infarction. Results from a community hospital.

Emergency coronary angioplasty was performed in 127 patients presenting to a community hospital with acute myocardial infarction. Reperfusion and successful dilatation were performed in 117 patients (92%) at 3.3 +/- 1.8 hours from the onset of pain. Eleven patients (8.6%) died, ten patients (7.9%) developed reocclusion, and ten patients (7.9%) required coronary bypass surgery during the initial hospitalization. Late restenosis occurred in 36% (27/76) of patients restudied or 27% (27/100) of patients at risk for restenosis. Ejection fraction improved in patients with patent vs occluded vessels (8.4% +/- 8.2% vs -4.1% +/- 6.0%) and improved most in anterior vs inferior vs posterolateral infarcts (11.0% +/- 8.4% vs 6.8% +/- 6.4% vs 2.6% +/- 7.5%). Posthospitalization follow-up in all patients (mean, 13.4 months) revealed only one late death. Of the patients followed up, 83% had no angina, and 17% of patients had mild angina. Our experience demonstrates that coronary angioplasty for acute myocardial infarction can be performed in the community hospital by an experienced cardiovascular laboratory team with a high success rate, a low reocclusion rate, an improvement in ejection fraction, and an excellent long-term prognosis. The community hospital setting allows early access to patients and creates the potential for early reperfusion and myocardial salvage.

Acute Disease↗
PubMed1985

Long term prognosis of recurrent haematuria.

A long term follow up study of 100 children referred with recurrent haematuria for at least one year to two regional paediatric nephrology units is described. The mean duration of follow up was 8.2 years. An adequate renal biopsy was obtained in 96 and eight cases of Alport's syndrome and 10 of IgA nephropathy were diagnosed (20% and 26% respectively of the biopsies examined by electron microscopy and immunofluorescence). Five patients developed end stage renal failure and six hypertension requiring treatment, with the occurrence of these complications increasing progressively with increasing duration of follow up (1% at five years compared with 12% at 10 years). Adverse prognostic features were persistence of microscopic haematuria, proteinuria at presentation, and appreciable changes on renal biopsy. Eighty four patients had first degree relatives tested for haematuria; 30% of these families had another affected member. With long term follow up recurrent haematuria is associated with considerable morbidity and potential mortality.

Adolescent↗
PubMed1983

Blood testing compared with urine testing in the long term control of diabetes.

A comparison of visually read glucose oxidase strips and urine testing is reported in an unselected group of 19 diabetic children in relation to the degree of control achieved and to its acceptability. The degree of control was at least as good after five months' blood glucose monitoring at home (mean blood glucose 9.3 +/- SEM 2.9 mmol/l, mean 24 hour glucose excretion 113 +/- SEM 168 mmol/l) as after five months' urine testing (mean blood glucose 11.1 +/- SEM 4.1 mmol/l, mean 24 hour glucose excretion 141 +/- SEM 98 mmol/l). Home blood glucose monitoring was preferred either alone or in conjunction with urine testing in most cases.

Adolescent↗
PubMedDate not supplied

Factors that predict improvement in left ventricular ejection fraction after coronary angioplasty for acute myocardial infarction.

Acute and follow-up angiograms were analyzed in 75 patients with acute myocardial infarction treated with emergency coronary angioplasty to determine factors that might predict improvement in left ventricular ejection fraction. Ejection fraction improved 8.4 +/- 8.2% in 60 patients who maintained patent infarct vessels at follow-up angiography, compared with -4.1 +/- 6.0% in 15 patients who developed reocclusion (p less than .001). In patients with patent infarct vessels, univariate analysis revealed the following significant predictors of improvement in ejection fraction: initial ejection fraction (r = -.38, p less than .003) subtotal vs total stenosis (12.9 +/- 9.3% vs 6.9 +/- 7.3%, p less than .02), infarct vessel (left anterior descending 11.0 +/- 8.4%, right 6.8 +/- 6.4%, circumflex 2.6 +/- 7.5%, p less than .02), and time to follow-up study (less than or equal to 15 days vs greater than 15 days) (4.8 +/- 5.8% vs 9.8 +/- 8.6%, p less than .03). Reperfusion time (less than or equal to 2 hr vs greater than 2 hr) predicted improvement when subtotal stenoses and stuttering infarctions were excluded (10.6 +/- 7.0% vs 4.9 +/- 6.9, p less than .03). Multivariate analysis showed initial ejection fraction and subtotal vs total stenosis to be independent predictors. Patients with anterior infarctions, low initial ejection fractions, and subtotal stenoses or reperfusion times less than or equal to 2 hr are likely to benefit most from coronary angioplasty for acute myocardial infarction.

Angioplasty, Balloon↗