Biomedical subjects

G J Hunter

Publications and source records attributed to G J Hunter.

13 recordsLinked to original sources

PubMed1991

Regulation of filamentous bacteriophage length by modification of electrostatic interactions between coat protein and DNA.

Bacteriophage fd gene VIII, which encodes the major capsid protein, was mutated to convert the serine residue at position 47 to a lysine residue (S47K), thereby increasing the number of positively charged residues in the C-terminal region of the protein from four to five. The S47K coat protein underwent correct membrane insertion and processing but could not encapsidate the viral DNA, nor was it incorporated detectably with wild-type coat proteins into hybrid bacteriophage particles. However, hybrid virions could be constructed from the S47K coat protein and a second mutant coat protein, K48Q, the latter containing only three lysine residues in its C-terminal region. K48Q phage particles are approximately 35% longer than wild-type. Introducing the S47K protein shortened these particles, the S47K/K48Q hybrids exhibiting a range of lengths between those of K48Q and wild-type. These results indicate that filamentous bacteriophage length (and the DNA packaging underlying it) are regulated by unusually flexible electrostatic interactions between the C-terminal domain of the coat protein and the DNA. They strongly suggest that wild-type bacteriophage fd makes optimal use of the minimum number of coat protein subunits to package the DNA compactly.

Amino Acid Sequence↗

PubMed1991

Proton NMR imaging of cerebral blood flow using H2(17)O.

Cerebral blood flow was quantitatively mapped by monitoring the cerebral washout of H2(17)O using rapid, single-shot proton NMR imaging. H2(17)O acts as a freely diffusible contrast agent for proton imaging via its scalar-coupled term, enhancing T2 relaxation. Measured values for CBF ranged from 29 to 106 ml/min/100 g over a range of arterial pCO2 between 23 and 81 Torr.

Animals↗

PubMed1988

Variable electrostatic interaction between DNA and coat protein in filamentous bacteriophage assembly.

A restriction fragment carrying the major coat protein gene (gene VIII) was excised from the DNA of the class I filamentous bacteriophage fd, which infects Escherichia coli. This fragment was cloned into the expression plasmid pKK223-3, where it came under the control of the tac promoter, generating plasmid pKf8P. Bacteriophage fd gene VIII was similarly cloned into the plasmid pEMBL9+, enabling it to be subjected to site-directed mutagenesis. By this means the positively charged lysine residue at position 48, one of four positively charged residues near the C terminus of the protein, was turned into a negatively charged glutamic acid residue. The mutated fd gene VIII was cloned back from the pEMBL plasmid into the expression plasmid pKK223-3, creating plasmid pKE48. In the presence of the inducer isopropyl-beta-D-thiogalactoside, the wild-type and mutated coat protein genes were strongly expressed in E. coli TG1 cells transformed with plasmids pKf8P and pKE48, respectively, and the product procoat proteins underwent processing and insertion into the E. coli cell inner membrane. A net positive charge of only 2 on the side-chains in the C-terminal region is evidently sufficient for this initial stage of the virus assembly process. However, the mutated coat protein could not encapsidate the DNA of bacteriophage R252, an fd bacteriophage carrying an amber mutation in its own gene VIII, when tested on non-suppressor strains of E. coli. On the other hand, elongated hybrid bacteriophage particles could be generated whose capsids contained mixtures of wild-type (K48) and mutant (E48) subunits. This suggests that the defect in assembly may occur at the initiation rather than the elongation step(s) in virus assembly. Other mutations of lysine-48 that removed or reversed the positive charge at this position in the C-terminal region of the coat protein were also found to lead to the production of commensurately longer bacteriophage particles. Taken together, these results indicate direct electrostatic interaction between the DNA and the coat protein in the capsid and support a model of non-specific binding between DNA and coat protein subunits with a stoicheiometry that can be varied during assembly.

Bacteriophages↗

PubMed1988

Anomalous systemic venous drainage occurring in association with the hypogenetic lung syndrome.

A case in which anomalous systemic venous drainage occurred in association with the hypogenetic lung syndrome (scimitar syndrome) is described. The chest radiograph appearances of the anomalous systemic vein mimicked an anomalous pulmonary or scimitar vein. Angiography demonstrated that the patient also had a small anomalous pulmonary vein draining and a systemic artery supplying, the right lung. As the right lung was hypoplastic, all three features of the hypogenetic lung syndrome were present, in addition to partial anomalous systemic venous drainage.

Abnormalities, Multiple↗

PubMed1988

Demonstration of the ascending aorta in infective endocarditis by intravenous digital subtraction angiography.

Four patients with infective endocarditis were examined by digital subtraction angiography immediately before operation. In three a root abscess was suspected and the remaining patient was believed to have a false aneurysm at an infected aortic cannulation site. In all the cases digital subtraction angiography showed the structure in several projections and confirmed the presence of a cavity. Subsequent operation confirmed the site and nature of the lesions.

Adult↗

PubMed1987

Patterns of axillary lymphadenopathy demonstrated by mammography: implications for the asymptomatic woman in a breast screening programme.

Carcinoma of the breast is the commonest cause of mortality due to malignancy in women in England and Wales. Mammographic screening, with or without clinical examination, is being used increasingly to detect lesions at an earlier stage. In order to test the claim that an asymptomatic woman with axillary lymph nodes on mammography and no demonstrable underlying carcinoma has a greater than two-fold increased risk of developing subsequent breast cancer, a retrospective analysis was performed on 217 mammograms selected from approximately 40,000 screened women using a cluster sampling technique. A group of women with histologically proven breast carcinoma and two control groups were analysed. The incidence, site and pattern of axillary lymph nodes was compared in the three groups. The relative risk of the asymptomatic woman with axillary lymph nodes developing breast cancer was 1.08 times that of the asymptomatic woman without axillary lymph nodes. From these data we conclude that the presence of lymph nodes does not constitute a risk factor for the development of subsequent ipsilateral mammary cancer and should not influence the assessment of screening mammograms.

Adult↗

PubMed1987

Effects of nifedipine on coronary perfusion; recent assessment by parametric digital subtraction.

The effects of nifedipine on myocardial perfusion abnormalities were investigated in 6 patients with left coronary artery disease using a digital angiographic method. Selective left coronary angiograms were digitized on-line into a 256 x 256 pixel matrix, approximately 20 ECG-gated end-diastolic frames being acquired during each coronary injection. After background subtraction, parametric analysis was undertaken, measuring sequential changes in contrast opacification against time. Isochrone maps were derived showing the distribution of times to attainment of peak contrast density throughout the left ventricle (the Tmax image) reflecting myocardial perfusion, and of times to arrival of half peak opacification (the T1/2max image) as an index of coronary flow. At basal heart rate (fixed by pacing) mean Tmax was attained in well supplied myocardium at the 7th cardiac cycle, and at the 9th cardiac cycle in the least perfused territory. Overdrive pacing reduced arrival times by 2-3 cycles, but inhomogeneity persisted. After sublingual nifedipine, contrast arrival was significantly accelerated by a mean of two cardiac cycles in poorly perfused regions, and by one cardiac cycle elsewhere. After nifedipine, overdrive pacing shortened Tmax and T1/2max most markedly in the least supplied territory. Results with this new technique indicate that nifedipine has beneficial effects on regional malperfusion in coronary disease.

Aged↗

PubMed1987

99mTc DTPA scanning with diuretic washout. Is it useful in the investigation of obstruction in the presence of gross renal tract dilatation?

Diuretic-enhanced 99mTc DTPA renal scanning aims to determine whether or not a kidney is obstructed. In the presence of gross renal tract dilatation the validity of this technique is questioned. Twenty-eight patients (51 kidneys) with the prune belly syndrome, characterised by gross dilatation and tortuosity of the ureters, were studied. These patients underwent diuretic 99mTc DTPA scanning at the time of diagnosis and at yearly intervals thereafter. Long-term clinical follow-up (3 years) with serial serum creatinine was available in all children. In all cases renal function remained stable and on this basis urinary tract obstruction was excluded. Analysis of the first 99mTc DTPA scan included differential function, whole kidney mean transit time (WKMTT) and the time taken for tracer activity to fall to 75% of peak activity after diuretic stimulus (T75). Using the 99mTc DTPA scan, obstruction can be excluded if the WKMTT is less than 5 min or, in the presence of a prolonged WKMTT, if the diuretic stimulus results in a T75 of less than 5 min. A T75 of between 5 and 10 min is considered equivocal and a T75 exceeding 10 min means that obstruction cannot be excluded. 99mTc DTPA scanning, using these criteria for diagnosis, provided false positive information in 22 kidneys (43%). There were no false negatives. 99mTc DTPA scanning with diuretic washout, using WKMTT and T75 criteria, is not appropriate for the detection of renal tract obstruction in the presence of marked upper renal tract dilatation, since the false positive rate of 43% is unacceptably high.

Adolescent↗

PubMed1986

Parametric imaging using digital subtraction angiography.

Digital subtraction angiography following an injection of iodinated contrast material can regularly produce good quality images. In addition to the conventional anatomical information, the timed sequence of digital images also contains useful temporal information which hitherto has been largely ignored. A simple method of image processing is described which utilises this timing information and presents it as a colour-coded set of functional images. Three parameters MAX, T-MAX and T-1/2 MAX are extracted from time-density curves, analogous to the time-activity curves of Nuclear Medicine, on a pixel-by-pixel basis. These parameters are used as a measure of overall organ perfusion, blood transit time between different vascular compartments, and as an indication of the initial delivery of contrast material to an organ. They have found use in the analysis of myocardial perfusion, before and after pharmacological intervention, and in the examination of the cerebral and renal circulations. The potential advantages of this technique derive from its superior spatial, temporal and contrast resolution.

Angiography↗

PubMed1985

Cholecystokinin cholecystography: a three year prospective trial.

A prospective study was undertaken to assess whether or not cholecystokinin cholecystography was able to predict the long-term results of cholecystectomy. The patients studied were all suffering from abdominal pain which was thought to be biliary in nature but in whom standard oral cholecystography did not reveal gall-bladder disease. There were 48 patients, mostly female, who were followed for 3 or more years after investigation and treatment. Half of the patients underwent cholecystectomy. There was no difference in outcome between those patients treated conservatively and those who underwent cholecystectomy. Cholecystokinin cholecystography was unable to predict the response of the patient to surgery in respect of relief of pain. It is concluded that cholecystokinin cholecystography is not a useful investigation when considering whether or not cholecystectomy would benefit the patient and afford lasting relief from pain.

Adult↗

PubMed1985

Digital subtraction angiography in coronary artery bypass graft assessment: clinical applicability.

Application of electrocardiogram gated digital subtraction angiography to the assessment of coronary artery bypass graft function was studied one week to eight years after bypass operation in ten unselected patients with recurrent chest pain. For the digital method, contrast was injected into the ascending aorta via a 4 or 5 French gauge catheter. The results of this technique were compared with those of selective graft and coronary angiography in the same patients by two independent observers. Of twenty six grafts in the series, patency was confirmed in twenty one by both selective and digital angiography. The quality of graft run off, graded by each observer using a simple scoring system, demonstrated six points of inter observer disagreement when standard cineangiograms were used, compared with nine points of disagreement when digital images were used. Digital subtraction angiography provided useful graft visualisation, but was less good than conventional angiography at defining the native coronary circulation. The role of this promising new technique has yet to be established.

Aged↗

PubMed1985

In vivo transcription of ribosomal RNA in relation to the mitotic cycle in Physarum polycephalum.

We have investigated the transcription of ribosomal RNA in plasmodia of Physarum polycephalum by a combination of pulse-labelling with [3H]uridine and RNA:DNA hybridization. The DNA used for the hybridization was a HindIII restriction fragment (cloned in bacteriophage lambda) of Physarum ribosomal DNA that carries a substantial fraction of the rRNA genes, enabling the ribosomal transcripts in the newly synthesized RNA to be measured. We found that ribosomal RNA constituted about 40% of the pulse-labelled RNA at all times during the synchronous mitotic cycle.

DNA↗

PubMedDate not supplied

Interactions between DNA and coat protein in the structure and assembly of filamentous bacteriophage fd.

Bacteriophage fd is a class I filamentous virus (others are M13 and f1) that comprises a circular, single-stranded DNA molecule enclosed in a cylindrical protein sheath to form a flexible particle approximately 890 nm long and 7 nm in diameter. The viral DNA contains 6,408 nucleotides incorporating 10 genes, and the protein sheath is composed of about 2,700 major coat protein subunits in a shingled helical array, the symmetry of which is defined by a fivefold rotational axis combined with a twofold screw axis of pitch 3.2 nm. The DNA extends throughout the length of the particle but is not base-paired and has a symmetry different from that of the protein helix. How the DNA is packed remains unclear but the number (2.4) of nucleotides packaged per major coat protein subunit is certainly not integral, in contrast with, say, the packaging of RNA in tobacco mosaic virus. The coat protein subunit is 50 amino-acid residues in length and, in the virus particle, adopts a largely alpha-helical conformation, with the long axis of the helix aligned close to the long axis of the filament. This protein is arranged with its negatively charged N-terminal region on the outside of the filament and its positively charged C-terminal region on the inside abutting the DNA. We report here that positive charge on one of the four lysine side chains in the latter region has a direct effect on DNA packaging, because when this charge is absent, elongated particles are produced with lengths that can be correlated with the residual positive charge in the C-terminal region of the coat protein subunit.

Amino Acid Sequence↗