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Biomedical subjects

A Chambers

Publications and source records attributed to A Chambers.

At least 37 records · Page 2Linked to original sources
PubMed1989

Characterization of the transcriptional potency of sub-elements of the UAS of the yeast PGK gene in a PGK mini-promoter.

The upstream activator (UAS) of the yeast PGK gene comprises three different sequence elements. These are 1) a region of strong protein binding called the YFP, 2) three repeats of the motif CTTCC and 3) an essential activator core (AC) sequence that binds the protein RAP1. To assess the function of each of these elements in transcriptional activation we have inserted them individually and in various combinations into a PGK mini-promoter. This comprises only the transcription initiation elements from the PGK promoter and is inactive in the absence of activator sequences. None of the individual sequence elements was capable of activating the mini-promoter. However either the YFP or the CTTCC boxes in conjunction with the AC box resulted in efficient expression. Transcription levels were not however as high as when all three elements were inserted. These data suggest that the efficiency of PGK transcription depends upon the interactions between three different sequences. Furthermore while RAP1 per se is not a transcriptional activator it can associate promiscuously with other factors to create a functional transcription complex.

Base Sequence↗
PubMed1989

HIV-1 TAT "activates" presynthesized RNA in the nucleus.

Replication of the human immunodeficiency virus (HIV-1) depends upon the viral TAT protein. TAT stimulates gene expression via a target response sequence (TAR) located within the HIV-1 LTR. As TAR is located in the transcribed region it could act as a signal in either the DNA, the RNA, or both. To test whether TAT acts on transcription and/or posttranscriptionally, we produced TAT in yeast and monitored its activity after microinjection into the nucleus or cytoplasm of Xenopus oocytes. The TAT protein stimulated TAR-dependent expression, but this activation was not inhibited by transcriptional inhibitors. Furthermore, TAR-containing RNA, produced in vitro, was "activated" by TAT after coinjection into oocytes. This activation only occurred, however, when the RNA was injected into the nucleus and not into the cytoplasm. Our data indicate, therefore, that in the Xenopus system TAT acts on presynthesized RNA and that the nucleus is involved in this action.

Animals↗
PubMed1989

Transcriptional control of the Saccharomyces cerevisiae PGK gene by RAP1.

The promoter of the yeast glycolytic gene encoding phosphoglycerate kinase (PGK) contains an upstream activation sequence between bases -538 and -402 upstream of the initiating ATG. The upstream activation sequence contains multiple functional elements, including an essential region called the activator core (AC) sequence and three copies of the pentamer 5'-CTTCC-3'. The AC sequence shows strong homology to the consensus binding sites for the yeast proteins RAP1 (GRF1) and TUF. We have demonstrated that the yeast protein which interacts with the AC sequence is the DNA-binding protein RAP1. Expression of the PGK gene is found to be regulated according to the carbon source in the growth medium. PGK mRNA levels are high in yeast cells grown in glucose medium but low in yeast cells grown in media containing carbon sources such as pyruvate and acetate. This carbon source regulation of transcription was found to be mediated, in part, via regulation of RAP1 binding to the AC sequence. The promoters of many other yeast glycolytic genes also contain consensus RAP1-binding sites and copies of the CTTCC pentamer. This suggests that RAP1 may be involved in transcriptional control of many other glycolytic genes in addition to the PGK gene.

Antibodies↗
PubMed1989

Comparison of a lactose-free formulation of sodium cromoglycate and sodium cromoglycate plus lactose in the treatment of asthma.

A double-blind, parallel group, 7-centre trial was carried out to compare the clinical efficacy and patient acceptability of two formulations of sodium cromoglycate for inhalation in patients suffering from asthma. Each single-dose capsule for use in a breath-actuated inhaler contained either a blend of sodium cromoglycate (20 mg) plus lactose (20 mg) or a lactose-free pelletized formulation of sodium cromoglycate (20 mg). Data were summarized from 529 asthmatic patients who had been using the blend formulation for at least 3 months previously. Two hundred and sixty-five patients then received pelletized sodium cromoglycate and 264 patients remained on sodium cromoglycate plus lactose for at least 3 months. Regular assessments were made by patients and clinicians during the trial period of treatment effectiveness. No clinically significant differences were observed between the two formulations after 3 months on test treatment. After a treatment period of 6 months, the pelletized formulation was shown to have some advantages over the blend formulation which were not observed at 3 months, with a significantly higher proportion of 'very effective' assessments being recorded by both patients and clinicians. The capsules of pelletized sodium cromoglycate required significantly less inhalations to empty compared to the capsules of the blend. No differences were observed between the two formulations with regard to the incidence of transient cough and throat irritation after inhalation.

Adolescent↗
PubMed1988

The UAS of the yeast PGK gene is composed of multiple functional elements.

The UAS (upstream activator sequence) of the yeast PGK gene contains a transcriptional activator domain located between bases -479 and -402 upstream from the initiating ATG. This region of the UAS contains three direct repeats of the sequence 5'CTTCC3'. The roles in transcriptional activation of these repeats and other sequences within the activator domain were investigated. When short regions containing the repeats were removed PGK expression was considerably reduced, the magnitude of the effect depended upon which CTTCC block was absent. Sequences between -473 and -458 which did not contain a CTTCC block were also shown to be necessary for high levels of PGK expression. A DNA fragment containing activator sequences up to -473 was shown to interact specifically in vitro with a yeast nuclear protein extract. DNase I footprinting identified a protected region between -473 and -458 and single base changes in DNase I sensitivity at the CTTCC repeats.

Chromosome Deletion↗
PubMed1988

Molecular cloning and chromosomal localization of a gene coding for human cardiac myosin heavy-chain.

A human cardiac myosin heavy-chain (MHC) gene, cloned in a charon 4A phage, was isolated using two rat cardiac pCMHC DNA clones (pCMHC26: alpha-MHC type; and pCMHC5: beta-MHC type) as probes and shown to correspond to cardiac myosin heavy-chain of the alpha-type. The 4.3-KB cardiac genomic DNA clone was used as a probe in the Southern analysis of human genomic DNA from human-Chinese hamster or human-mouse somatic cell hybrids. The results show that the human cardiac MHC gene is assigned to chromosome 14 and the human cardiac and skeletal MHC genes do not cosegregate as do the mouse cardiac and skeletal MHC genes.

Chromosome Mapping↗
PubMed1988

RNA 3' cleavage and polyadenylation in oocytes and unfertilized eggs of Xenopus laevis.

Xenopus laevis histone H4 and H1 genes were transcribed in vitro to generate artificial precursor mRNAs (pre-mRNAs). These pre-mRNAs were microinjected into oocytes, matured oocytes, and unfertilized eggs of Xenopus laevis and their 3' cleavage and polyadenylation were investigated. In the oocyte nucleus both H4 and H1 pre-mRNAs were 3' cleaved but were not detectably polyadenylated. In the oocyte cytoplasm there was neither 3' cleavage nor polyadenylation of these histone pre-mRNAs. When injected into either matured oocytes or unfertilized eggs, the pre-mRNAs underwent 3' cleavage but this was inefficient when compared to the oocyte nucleus. In addition approximately 50% of the remaining uncleaved pre-mRNA was subject to a polyadenylation activity which added A tails of approximately 70 A residues. In contrast, artificial mouse beta-globin pre-mRNAs were not detectably 3' cleaved or polyadenylated in either microinjected oocytes or unfertilized eggs.

Animals↗
PubMed1985

Individual Xenopus histone genes are replication-independent in oocytes and replication-dependent in Xenopus or mouse somatic cells.

We have assessed the response of many histone H3 mRNAs and an H1C mRNA in Xenopus tissue culture cells after treatment with the DNA synthesis inhibitor hydroxyurea. The amount of the histone mRNAs falls rapidly in response to the inhibitor. This response is prevented by cycloheximide. Cloned Xenopus histone genes were transfected into mouse cells and a cell line was obtained in which the Xenopus genes were actively expressed giving rise to mRNA with correct 5'-termini. The Xenopus genes were correctly regulated at the level of mRNA amounts in the mouse cell line. Nuclear microinjection experiments with Xenopus oocytes and S1 nuclease analysis of normal ovary RNA showed that the H1C gene, and probably also two H3 genes, which are replication-dependent in somatic cells are expressed in oocytes and are therefore replication-independent in this cell type. The same promoters are used in both replication-dependent and independent expression.

Amino Acid Sequence↗
PubMed1977

Correlation of platelet aggregation, plasma factor activity, and megathrombocytes in diabetic subjects with an without vascular disease.

Second-phase platelet aggregation induced by adenosine diphosphate (ADP) and epinephrine was measured in fasting platelet-rich plasma in normals, "prediabetics," and diabetics with or without vascular disease. "Plasma factor" potentiation of ADP-induced second-phase platelet aggregation was also estimated, as were megathrombocyte numbers in the same patient groups. There was an increased sensitivity of second-phase platelet aggregation noted with both aggregating agents in all diabetic groups except for the prediabetics. This activity was paralleled by an increase in plasma factor activity. In vivo evidence of an increased turnover of platelets in frank diabetics was suggested by increased numbers of megathrombocytes. These studies demonstrate that platelets from diabetics are sensitive to aggregating agents and that this sensitivity may be related to plasma factor(s) present in diabetics. In vivo platelet aggregation may be present in diabetics. Longitudinal studies will be necessary to establish the relationship of these findings to the genesis of diabetic vascular disease.

Adult↗
PubMed1976

Benzodipyran derivatives with antiallergic activity.

The synthesis and antiallergic activity of a number of benzodipyrandicarboxylic acids are described. Antiallergic activity of the compounds was determined using the homologous passive cutaneous anaphylaxis (PCA) reaction in the rat. The structural requirements for activity in the PCA screen are discussed. In this test system the linear benzodipyrans are more active than their angular analogues.

Animals↗
PubMed1975

Inhibition of labile aggregation-stimulating substance (LASS) and platelet aggregation in diabetes mellitus.

Irreversible second-phase aggregation of platelets in diabetic patients is prevented in vitro by 5, 8, 11, 14-eicosatetraynoic acid (TYA), a competitive inhibitor of the labile aggregation-stimulating substance (LASS) which is formed from arachidonic acid. Thus, inhibition of prostaglandin synthesis inhibits platelet aggregation in diabetic subjects. These findings indicate that platelets from diabetics are subject to control by intracellular mechanisms operative in the regulation of platelet function in normal individuals.

5,8,11,14-Eicosatetraynoic Acid↗