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Biomedical subjects

A Bell

Publications and source records attributed to A Bell.

At least 163 records · Page 9Linked to original sources
PubMed1990

Mutations that alter the ability of the Escherichia coli cyclic AMP receptor protein to activate transcription.

The effects of a number of mutations in the E. coli cyclic AMP receptor protein (CRP) have been determined by monitoring the in vivo expression and in vitro open complex formation at two semi-synthetic promoters that are totally CRP-dependent. At one promoter the CRP-binding site is centered around 41.5 base pairs upstream from the transcription start whilst at the other promoter it is 61.5 base pairs upstream. The CRP mutation E171K reduces expression from both promoters whilst H159L renders CRP totally inactive: neither mutation stops CRP binding at either promoter. The mutations K52N and K52Q reverse the effect of H159L and 'reeducate' CRP to activate transcription. CRP carrying both H159L and K52N activates transcription from the promoter with the CRP site at -41.5 better than wild type CRP. In sharp contrast, this doubly changed CRP is totally inactive with respect to the activation of transcription from the promoter carrying the CRP site at -61.5. Our results suggest that CRP can use different contacts and/or conformations during transcription activation at promoters with different architectures.

Amino Acid Sequence↗
PubMed1990

Stringent spacing requirements for transcription activation by CRP.

The cyclic AMP receptor protein-cAMP complex (CRP-cAMP) binds at a variety of distances upstream of several E. coli promoters and activates transcription. We have constructed a model system in which a consensus CRP binding site is placed at different distances upstream of the melR promoter. CRP-cAMP activates transcription from melR when bound at a number of positions, all of which lie on the same face of the DNA helix. The two distances at which transcription is strongly activated correspond exactly to those at which CRP-cAMP binds upstream of the well-studied galP1 and lac promoters. Footprinting of the synthetic promoters reveals that RNA polymerase makes identical contacts with their -10 regions even though CRP-cAMP binds at a different distance in each case. Kinetic analysis in vitro indicates that CRP-cAMP activates transcription from these promoters in similar but distinct ways. A model is proposed to explain this two-position activation.

Base Sequence↗
PubMed1990

Thyroid hormone and dietary carbohydrate interact to regulate rat liver S14 gene transcription and chromatin structure.

Dietary carbohydrate and thyroid hormone (T3) interact to regulate rat liver S14 gene expression. The molecular basis for this interaction was examined by analysis of hepatic mRNAS14 levels, S14 gene transcription, and chromatin structure. While starvation of euthyroid rats inhibited hepatic S14 gene transcription greater than or equal to 90%, sucrose administration induced mRNAS14 and S14 transcription to 82% of euthyroid-fed levels within 4 h. In contrast, administration of sucrose or T3 to starved hypothyroid animals restored S14 gene transcription to only 30% of euthyroid-fed values. Both T3 and sucrose were required to restore S14 run-on activity and mRNAS14 to euthyroid-fed levels within 4 h. Thus, T3 and sucrose interact synergistically and rapidly to induce S14 gene transcription. Analysis of S14 chromatin structure showed that starvation of hypothyroid rats inhibited the formation of three DNase I-hypersensitive sites flanking the 5'-end of the S14 gene (Hss-1 at -65 to -265 base pairs; Hss-2 at -1.2 kilobases and Hss-3 at -2.67 kilobases). The loss of these sites correlated with the repression of S14 gene transcription in starved hypothyroid rats. Whereas administration of sucrose to starved hypothyroid rats consistently induced the Hss-1 and Hss-2 sites, T3 consistently induced all three DNase I-hypersensitive sites. Yet, neither treatment alone induced S14 gene transcription to euthyroid levels. The combination of T3 and sucrose induced no additional change in S14 chromatin structure over that induced by T3 alone. Thus, regulation of S14 chromatin structure alone is not the sole mechanism by which these stimuli regulate S14 gene transcription. We speculate that the synergistic regulation of S14 gene transcription by T3 and dietary carbohydrate involves a complex interaction between factors which regulate the accessibility of putative cis-regulatory elements through changes in chromatin structure and the regulation of "transcription factors" which interact with these elements.

Animals↗
PubMed1990

Comparison of promoter activities in Escherichia coli and Pseudomonas aeruginosa: use of a new broad-host-range promoter-probe plasmid.

The broad-host-range plasmid, pRW2, is a derivative of pRK 2501 carrying the Escherichia coli lac operon without a promoter, downstream of a polylinker sequence. We have cloned a number of DNA fragments carrying promoters into this plasmid and measured promoter activity in both E. coli and Pseudomonas aeruginosa. Promoters carrying consensus -10 and -35 sequences were active in both backgrounds and the dependence of activity on the nucleotide sequence of the 35 region was the same in both cases. We also measured the activity of two promoters at which transcription in E. coli was totally dependent on the E. coli activators CRP and FNR: both promoters were found to be active in P. aeruginosa.

Base Sequence↗
PubMed1990

Prospective study of the value of ultrasound measurements in the diagnosis of acute rejection following renal transplantation.

In this prospective study we have used ultrasonographic measurements of the cross-sectional area of transplanted kidneys, as an objective assessment of graft size, for diagnosis of acute rejection episodes. Sixty episodes of acute graft dysfunction (serum creatinine rise of greater than or equal to 30 mumol/l) were studied in 40 patients. Tru-Cut biopsy under ultrasound control was performed in all cases and 36 episodes of acute cellular rejection were identified. An increase in graft cross-sectional area of greater than or equal to 10 per cent was defined as a positive scan, indicative of an acute rejection episode. Using these criteria, ultrasound correctly diagnosed rejection in 29 out of 36 cases (sensitivity 81 per cent) and there were four false positive results (specificity 83 per cent). The investigation had a predictive value of 88 per cent when positive and 74 per cent when negative.

Graft Rejection↗
PubMed1990

The effect of nimodipine on outcome after head injury: a prospective randomised control trial. The British/Finnish Co-operative Head Injury Trial Group.

To study the effect of nimodipine on the outcome of head injury, three hundred and fifty-two patients who were not obeying commands were randomised to placebo or nimodipine (2 mg per hour intravenously for 7 days). The 2 groups were well matched for important prognostic features. Six months after injury, more of the patients who were given nimodipine had a favourable outcome (moderate/good recovery) than in the control group, but the increase in favourable outcome (8%) was not significant statistically.

Craniocerebral Trauma↗
PubMed1990

The fractional shortening-velocity ratio: validation of a new echocardiographic Doppler method for identifying patients with significant aortic stenosis.

Previous studies have shown that Doppler echocardiographic methods based on the continuity equation can accurately determine aortic valve area in patients with clinically significant aortic stenosis; nonetheless, methods based on the continuity equation are time-consuming and may not be technically possible in all subsets of patients. The purpose of this study was to develop and prospectively evaluate a simpler new noninvasive method for determining aortic valve area. With this new method, aortic valve area is obtained by dividing the percent fractional anteroposterior shortening at the midventricular level by 4V2, where V is the peak instantaneous Doppler-derived flow velocity across the aortic valve. In the first part of the study, the fractional shortening-velocity ratio was used to examine a group of 25 patients evaluated retrospectively. There was a highly significant linear relation between the fractional shortening-velocity ratio (FSVR) and the aortic valve area (AVA) determined by the Gorlin formula at cardiac catheterization: FSVR = 1.1(AVA) - 0.1 (r = 0.88; significance of slope p less than 0.001). Furthermore, a fractional shortening-velocity ratio less than 1.1 reliably identified all patients with clinically significant aortic stenosis (aortic valve area less than 1 cm2), whereas a fractional shortening-velocity ratio less than 0.8 reliably identified all patients with critical aortic stenosis (aortic valve area less than 0.7 cm2). This new method was then validated by prospectively applying the fractional shortening-velocity ratio to a group of 44 patients from two separate institutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗
PubMed1990

Insulin rapidly induces rat liver S14 gene transcription.

We evaluated the role insulin plays in the regulation of hepatic S14 gene transcription using the streptozotocin-induced diabetic rat model. Nuclear run-on activity and mRNAS14 levels were reduced by more than 85% in diabetic rats compared to those in intact animals. After the administration of insulin, both S14 run-on activity and mRNAS14 levels were rapidly induced. Within 1 h of insulin administration, S14 run-on activity and mRNAS14 were induced 5- and 8-fold, respectively. S14 gene expression was restored to intact levels within 4 h, with overall increases in run-on activity and mRNAS14 of 7- and 20-fold, respectively. The full induction of mRNAS14 cannot be accounted for solely by activation of S14 gene transcription, implicating insulin effects at the posttranscriptional level. However, our results show that the principal target for insulin action on the S14 gene is transcriptional. Administration of dibutryl cAMP and theophylline fully blocked the insulin-mediated increase in S14 gene transcription, indicating that hepatic cAMP levels play a dominant negative role in regulating S14 gene transcription in vivo. Fructose administration to starved diabetic rats induced only a marginal 60% increase in mRNAS14 and S14 run-on activity within 4 h, while insulin plus fructose or insulin plus glucose fully restored S14 gene expression to intact levels within the same time period. Thus, dietary fructose or a metabolite generated from fructose alone cannot induce S14 gene transcription or mRNAS14 to intact levels in the starved diabetic rat. Acute effects of dietary carbohydrate on hepatic S14 gene transcription are insulin dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Safety first.

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Accident Prevention↗