PubMed Health⌕ Search

Biomedical subjects

R W Lucas

Publications and source records attributed to R W Lucas.

13 recordsLinked to original sources
PubMed2001

Crystallization of Brome mosaic virus and T = 1 Brome mosaic virus particles following a structural transition.

Brome mosaic virus (BMV), a T = 3 icosahedral plant virus, can be dissociated into coat protein subunits and subunit oligomers at pH 7.5 in the presence of concentrated salts. We have found that during the course of this treatment the coat protein subunits are cleaved, presumably by plant cell proteases still present in the preparation, between amino acids 35 and 36. The truncated protein subunits will then reorganize into T = 1 icosahedral particles and can be crystallized from sodium malonate. Quasi elastic light scattering and atomic force microscopy results suggest that the transition from T = 3 to T = 1 particles can occur by separate pathways, dissociation into coat protein subunits and oligomers and reassembly into T = 1 particles, or direct condensation of the T = 3 virions to T = 1 particles with the shedding of hexameric capsomeres. The latter process has been directly visualized using atomic force microscopy. Native T = 3 virions have been crystallized in several different crystal forms, but neither a rhombohedral form nor either of two orthorhombic forms diffract beyond about 3.4 A. Tetragonal crystals of the T = 1 particles, however, diffract to at least 2.5 A resolution. Evidence suggests that the T = 1 particles are more structurally uniform and ordered than are native T = 3 virions. A variety of anomalous virus particles having diverse sizes have been visualized in preparations of BMV used for crystallization. In some cases these aberrant particles are incorporated into growing crystals where they are frequently responsible for defect formation.

Bromovirus↗
PubMed1999

Xanthine phosphoribosyltransferase from Leishmania donovani. Molecular cloning, biochemical characterization, and genetic analysis.

Xanthine phosphoribosyltransferase (XPRT) from Leishmania donovani is a unique enzyme that lacks a mammalian counterpart and is, therefore, a potential target for antiparasitic therapy. To investigate the enzyme at the molecular and biochemical level, a cDNA encoding the L. donovani XPRT was isolated by functional complementation of a purine auxotroph of Escherichia coli that also harbors deficiencies in the prokaryotic phosphoribosyltransferase (PRT) activities. The cDNA was then used to isolate the XPRT genomic clone. XPRT encodes a 241-amino acid protein exhibiting approximately 33% amino acid identity with the L. donovani hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and significant homology with other HGPRT family members. Southern blot analysis revealed that XPRT was a single copy gene that co-localized with HGPRT within a 4.3-kilobase pair (kb) EcoRI fragment, implying that the two genes arose as a result of an ancestral duplication event. Sequencing of this EcoRI fragment confirmed that HGPRT and XPRT were organized in a head-to-tail arrangement separated by an approximately 2.2-kb intergenic region. Both the 3.2-kb XPRT mRNA and XPRT enzyme were significantly up-regulated in Deltahgprt and Deltahgprt/Deltaaprt L. donovani mutants. Genetic obliteration of the XPRT locus by targeted gene replacement indicated that XPRT was not an essential gene under most conditions and that the Deltaxprt null strain was competent of salvaging all purines except xanthine. XPRT was overexpressed in E. coli and the recombinant protein purified to homogeneity. Kinetic analysis revealed that the XPRT preferentially phosphoribosylated xanthine but could also recognize hypoxanthine and guanine. K(m) values of 7.1, 448.0, and >100 microM and k(cat) values of 3.5, 2.6, and approximately 0.003 s(-1) were calculated for xanthine, hypoxanthine, and guanine, respectively. The XPRT gene and XPRT protein provide the requisite molecular and biochemical reagents for subsequent studies to validate XPRT as a potential therapeutic target.

Amino Acid Sequence↗
PubMed1999

Surface processes in the crystallization of turnip yellow mosaic virus visualized by atomic force microscopy.

In situ atomic force microscopy (AFM) was used to investigate surface evolution during the growth of single crystals of turnip yellow mosaic virus (TYMV). Growth of the (101) face of TYMV crystals proceeded by two-dimensional nucleation. The molecular structure of the step edges and adsorption of individual virus particles and their aggregates on the crystalline surface were recorded. The surfaces of individual virions within crystals were visualized and seen to be quite distinctive with the hexameric and pentameric capsomers of the T = 3 capsids being clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a virus by AFM. In the course of recording the in situ development of the crystals, a profound restructuring of the surface arrangement was observed. This transformation was highly cooperative in nature, but the transitions were unambiguous and readily explicable in terms of an organized loss of classes of virus particles from specific lattice positions. In some cases areas of a single crystal surface were recorded in which were captured successive phases of the transition. We believe this provides the first visual record of a cooperative restructuring of the surface of a supramolecular crystal.

Capsid↗
PubMed1984

The logical description of a disease class as a Boolean function with special reference to the irritable bowel syndrome.

Although some disease classes can be defined by a single defining characteristic, in terms of traditional logic one that is both necessary and sufficient, other disease classes, such as the so-called "irritable bowel syndrome' (IBS), have only a set of symptoms, signs etc. which are said to characterize it in some undefined way. This characterization might be made definite by using simple Boolean algebra to give a logical description of the disease class. This method can only be used if the individual doctor can be shown to be consistent in his assignment of a set of data to the disease class and also if his assignment agrees independently with that of another doctor. To test such consistency and concordance, 100 case records were collected of supposed IBS and not-IBS; 20 of these were replicated to test consistency, and the total of 120 records was examined by five consultants independently, who assigned them either to an IBS or a not-IBS class. From the 1500 pair-wise comparisons, analysis revealed that the disagreement in assignment between doctors was only slightly greater than the disagreement within doctors, suggesting that the group of doctors acted as if there were an implicit description of IBS with which each of them broadly agreed. This implicit description, if made explicit, could form a basis for diagnosis by logical implication. This method of logical definition has general application in medicine and a set of defined cases could be used to establish entry criteria for multicentre trials of a previously ill-defined class.

Analysis of Variance↗
PubMed1980

Effectiveness of one-to-one health education in the home.

HEALTH education conventionally takes one of two forms, a mass campaign to the whole population using the media, or an approach to members of chosen at-risk groups, through individual or small group sessions. The following study explores the efficacy of one-to-one education of the whole adult population, at risk or not, by visiting a random sample of them in their homes and giving them information on one of four relevant topics, adapting the style and content to the individual's needs and interests. The survey therefore tests the technique of a flexible, person-orientated approach to health education.

Adult↗
PubMed1980

Knowledge of health information and services in a random sample of the population of Glasgow.

A RANDOM sample of adults in Glasgow was surveyed by trained interviewers to determine public knowledge on four topics chosen specifically for each of four age groups. The topics were: Welfare rights and services; Coronary Heart Disease (CHD) and individual action that can reduce risk; The dangers of smoking in pregnancy; and fluoride and its functions and the connections between good health and habitual behaviour.

Adult↗
PubMed1977

Psychiatrists and a computer as interrogators of patients with alcohol-related illnesses: a comparison.

A computer-administered 'interview' was developed for eliciting evidence relating to alcohol problems. Thirty-six volunteer male patients on their first visits to a specialist alcohol clinic were interviewed three times, by two psychiatrists and by the computer; information was sought about 72 pre-defined indicants concerning alcohol consumption, drinking behaviour, and symptoms. Each patient was asked to complete an attitude questionnaire anonymously. The extent of agreement between the evidence elicited by the computer and by the psychiatrists was quite high, and their estimated error rates were very similar, all between 10 per cent and 12 per cent in total. With respects to amounts of alcohol consumed, patients reported significantly greater amounts to the computer than they reported to the psychiatrists. The median amounts of pure ethanol consumed ranged from 1-19 kg per week calculated from reports made to one of the psychiatrists, up to 1-58 kg per week calculated from reports made to the computer. The results from the attitude questionnaire indicated a high level of acceptability to patients of computer interrogation.

Alcoholism↗
PubMed1976

Computer interrogation of patients.

A system of routine interrogation of patients using a computer has been developed. It includes a visual display unit with a specially designed response keyboard, and the program has been designed to adapt to the individual patient. The system was evaluated objectively, using the criteria of accuracy in eliciting symptoms, acceptability to the patient, and cost. While doctors will always take the ultimate management decisions, it seems that machines can be programmed to undertake the routine interrogation of patients, elicit evidence accurately and acceptably, and calculate the probabilities of disease as effectively as doctors.

Attitude↗