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S Humphries

Publications and source records attributed to S Humphries.

123 records · Page 7Linked to original sources
PubMed1979

Capsid protein precursor is one of two initiated products of translation of poliovirus RNA in vitro.

Previous studies in our laboratory have demonstrated that cell-free systems translating the Mahoney strain of poliovirus type I RNA utilize two unique initiation sites. In this study, defective-interfering particles of poliovirus, which contain deletions in the region encoding the capsid proteins, are shown to initiate translation of proteins in vitro at these same two sites. Both the standard virus and the defective-interfering virus RNA direct the synthesis of two polypeptides labeled with n-formyl-methionine (fmet) at their amino termini. The size of the smaller fmet polypeptide synthesized in vitro by the defective virus appears identical in size to that of the standard virus. However, the larger-molecular-weight fmet polypeptide is reduced in size from 115,000 to 69,000 daltons. This correlates exactly with the reduced size of the precursor to the capsid proteins synthesized by the defective virus in vivo and with the size of the deletion in the defective virus RNA (1,200 bases). This provides genetic evidence that the 115,000-dalton fmet polypeptide synthesized into vitro by the standard virus is NCVP1a, the precursor to the coat proteins. Although the identity of the small (5,000 to 10,000 daltons) fmet polypeptide is not clear, several lines of evidence enable us to exclude the possibility that it is VP4, the smallest viral capsid protein.

Capsid↗
PubMed1976

Mouse globin gene expression in erythroid and non-erythroid tissues.

Using cDNA hybridization, mouse globin RNA sequences can be detected in the nuclear and cytoplasmic RNA not only from erythroid cells (fetal liver and reticulocytes), but also in low amounts in non-erythroid tissues (adult brain and liver, and cultured lymphoma, untransformed, and transformed fibroblast cell lines). For the nuclear RNAs, melting curve, density, and size determinations on the hybrids confirmed the presence of an RNA species indistinguishable by cDNA hybridization from reticulocyte globin mRNA. Thus the genes coding for alpha- and beta-globin, proteins thought to be found only in a restricted range of differentiated cell types, may nonetheless be transcribed at very low levels in all mouse cells. The proportion of the globin RNA sequences in the nuclear RNA that are found associated with poly(A) sequences does not vary markedly from one tissue or cell line to another. In erythroid cells, however, the proportion of the cellular globin RNA sequences that are found in the cytoplasm is very much higher than in non-erythroid cells. This suggests the existence of messenger-specific nuclear post-transcriptional control mechanisms which do not use poly(A) as a signal, and which allow the cytoplasmic accumulation of globin mRNA only in erythroid tissues.

Animals↗
PubMedDate not supplied

Familial defective apolipoprotein B-100. Comparison with familial hypercholesterolemia in 18 cases detected in Munich.

It has recently been suggested that a substitution of glutamine for arginine at residue 3500 of apolipoprotein (apo) B-100 causes familial defective apo B-100 (FDB), an autosomal, dominantly inherited disorder, which leads to increased serum cholesterol levels. From a sample of 243 patients from Munich with type IIa hyperlipoproteinemia (HL), we have identified eight individuals with the apo B-100 arginine(3500)----glutamine mutation. In a group of 57 subjects with defective low density lipoprotein receptor (LDLR), no mutant apo B alleles were detected. The frequency of FDB in patients with type IIa HL was estimated to be 3%. In the kindreds of three of the probands, 10 additional carriers of the apo B mutation were identified. Clinical and biochemical data reveal a striking similarity between patients with FDB and those with a defect in the LDLR gene. Our data support previous findings that FDB is a serious disorder causing premature atherosclerosis.

Adult↗
PubMedDate not supplied

Genetic variation at the plasminogen activator inhibitor-1 locus is associated with altered levels of plasma plasminogen activator inhibitor-1 activity.

Plasminogen activator inhibitor-1 (PAI-1), a rapid inhibitor of tissue-type plasminogen activator, has been shown to be an independent risk factor for recurrent myocardial infarction (MI) at a young age. To investigate whether genetic variation in the PAI-1 gene is affecting plasma PAI-1 levels, a sample of 145 patients with an MI before the age of 45 years was genotyped for two polymorphisms at the PAI-1 locus, together with a sample of 95 healthy individuals of a similar age. All individuals were measured for plasma PAI-1 levels as well as for other fibrinolytic and metabolic risk indicators. A HindIII restriction fragment length polymorphism (RFLP) was used in this study in conjunction with a previously unreported eight-allele dinucleotide repeat polymorphism at the PAI-1 locus. The dinucleotide repeat polymorphism and HindIII RFLP were in strong linkage disequilibrium. There was no difference in the frequency of alleles of either polymorphism between patient and control groups. However, the smaller dinucleotide repeat alleles were significantly associated (p = 0.03) with higher plasma PAI-1 levels in the patient sample. This association was also apparent in the control sample but not at significant levels. Differences in regression coefficients for the effect of triglycerides on plasma PAI-1 levels suggest that triglyceride regulation of PAI-1 is genotype specific. Our data suggest that genetic variation at this locus contributes to between-individual differences in the level of plasma PAI-1, which is important in fibrinolysis and the pathogenesis of MI.

Adult↗
PubMedDate not supplied

Variation in the low density lipoprotein receptor gene is associated with differences in plasma low density lipoprotein cholesterol levels in young and old normal individuals from Italy.

We have used four restriction fragment length polymorphisms (RFLPs) of the human low density lipoprotein receptor (LDL-R) gene, detected by the restriction enzymes Ava II, Pvu II, and ApaLI (5' and 3'), to study the effect of variation at this gene locus in determining plasma cholesterol and LDL cholesterol levels. Two hundred eighty-nine normolipidemic individuals were studied from the Liguria region of Italy. The Pvu II RFLP was significantly associated with differences in plasma total and LDL cholesterol levels, explaining 9.6% of the sample variance in LDL cholesterol levels. The other RFLPs, which are in strong linkage disequilibrium with the Pvu II RFLP, were associated with smaller effects on LDL cholesterol. The Pvu II allele, distinguished by the presence of the variable cutting site (P2 allele), was associated with lower levels of total and LDL cholesterol, and the frequency of the P2 allele was significantly reduced in individuals with LDL cholesterol levels higher than the 75th percentile. The frequency of the P2 allele was significantly higher in the group of individuals over 65 years old, and in this group the P2 allele was also associated with a similar reduction in LDL cholesterol levels. Because of linkage disequilibrium, only four RFLP haplotypes were common in this sample. Of these, only the haplotype P2A2VI (relative frequency, 0.269) was associated with a reduction in LDL cholesterol (average excess, -11.5 mg/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

A common genetic polymorphism associated with lower coagulation factor VII levels in healthy individuals.

We have identified a genetic polymorphism of factor VII that is strongly associated with plasma factor VII coagulant activity (factor VIIc) in healthy individuals from the United Kingdom. This polymorphism was detected after Msp I digestion of polymerase chain reaction-amplified genomic DNA. In a sample of 284 men, the frequency of the M2 allele (loss of cutting site) is 0.1, and individuals with the M1M2 genotype have factor VIIc levels 22% below the sample mean (p less than 0.0001). Msp I genotype was found to be the strongest predictor of factor VIIc, accounting for 20.2% of the variance, with cholesterol accounting for an additional 3.5%. The base change that gives rise to the Msp I polymorphism is a G-to-A substitution in the codon for amino acid 353, leading to replacement of arginine (Arg) with glutamine (Gln) in the protein product of the M2 allele (designated Gln 353). Three individuals homozygous for the M2 allele have both low factor VIIc and low factor VII protein concentrations. The conformation of the Gln 353 molecule may be different from that of the Arg 353 protein, affecting its intracellular processing, secretion, turnover in plasma, or activity. In view of its association with lower factor VIIc levels, possession of the M2 allele may confer protection against thrombosis and myocardial infarction.

Aged↗
PubMedDate not supplied

Gene probes in diagnosis of familial hypercholesterolemia.

In the United Kingdom, about 5% of patients with familial hypercholesterolemia (FH) have a detectable deletion or rearrangement of part of the LDL-receptor gene, which results in the detection of shorter or abnormally sized fragments of the LDL-receptor gene in a Southern blot hybridization. This gene deletion can be used for following the inheritance of the defective gene and for diagnosis in the families of these individuals. In the families of the remaining patients, diagnosis may be possible using linked restriction fragment length polymorphisms (RFLPs) detected with the LDL-receptor probe. There are now 10 common RFLPs of the LDL-receptor gene, with variable sites in the 3' half of the gene. Over 80% of patients are heterozygous for at least one of these RFLPs, and, therefore, RFLPs are potentially informative for DNA diagnosis. For a fetus at risk of homozygous FH, antenatal diagnosis may also be possible using these methods. However, family studies require samples to be available from affected or unaffected relatives of the patient, and this limits the applicability of the tests. For some mutations, the base-pair change causing the defect in the LDL receptor itself creates or destroys a site for a restriction enzyme. Such "mutation-specific" RFLPs could be used for population screening, but, so far, such use has only been reported for the FH mutation common in Lebanon. In the future, it may be possible to develop mutation-specific oligonucleotide probes for the diagnosis of FH. These would be appropriate for screening populations or patients with hyperlipidemia. This information may also be useful if different mutations require different therapeutic strategies.

Cholesterol↗