Escherichia coli aspartate carbamoyltransferase: the probing of crystal structure analysis via site-specific mutagenesis

Crystal structures are known for aspartate carbamoyltransferase(ATCase) in the T and R states, with and without the allostericactivator adenosine triphosphate (ATP) or inhibitor cytidinetriphosphate (CTP). Visual inspection of X-ray crystal structuresdoes not provide all of the information necessary for the determinationof structure-function relationships in protein molecules. Thisproblem is compounded because the crystalline states of themolecule may introduce effects due to crystal packing, restrictedflexibility and less than optimum enzymatic conditions. Therefore,alternative techniques are required to test mechanisms conjecturedfrom three-dimensional crystal structures of proteins. The techniqueof site-specific mutagenesis allows the researcher to test structure- function models based on threedimensional structures and toobtain further insight into characteristics of the enzyme. Site-specificmutagenesis has been used to probe residues believed to be criticalin the structure and function of ATCase. Selection of residuesto be mutated has depended extensively on three-dimensionalcrystal structures of the enzyme. To date, 48 site-specificmutations at 37 different amino acid sites have been published.Although a total of 118 mutants at 58 different sites has beencommunicated to our laboratory, only published mutants willbe considered in this review. In this paper, we compile forthe first time, review, and analyze the site-specific mutantsof ATCase. Site-specific mutagenesis of proteins has becomea powerful technique in modern-day molecular biology, especiallyin studying a molecule as large as aspartate carbamoyltransferase.In this review, the role of site-specific mutagenesis of ATCaseis discussed and improvements in the analysis are suggested.     

The prevalence of common skin conditions in Australian school students: 3. acne vulgaris

Although viral warts are common, their exact frequency in the community is often underestimated and not well recorded. A random sample of 2491 students from schools throughout the State of Victoria, Australia were examined by dermatologists and dermatology registrars to record the prevalence of common, plantar and plane warts. The overall prevalence of warts adjusted for the age and sex of Victorian school children was 22% (95% confidence interval (CI) 20.1-20.7) varying from 12% (95% CI 9.4-15.7) in 4-6 year olds to 24% (95% CI 18.3-30.4) in 16-18 year olds. Common warts were the most frequent (16%) compared with plantar warts (6%) and plane warts (2%). There was no difference in the overall frequency of warts between males and females and there was no difference in frequency between those who had eczema and those who did not. Almost 40% of those found to have warts on examination had indicated on the survey questionnaire that they did not have any of these lesions. Of those who knew that they had warts, only 38% had used any treatment for them. These data, the first community-based prevalence data on warts ever published from Australia, confirm that warts are indeed common. They suggest the need for education programmes in schools on the nature of these lesions and the treatment available.     

Why we live and why we die

Several different techniques for urodynamic signal compression have been proposed in the last few years. Using these techniques it is possible to reduce the requirements for digital storage or transmission. There are a number of applications where it is essential to use such techniques in diagnostic and ambulatory urodynamics. The purpose of this study is to compare different techniques of urodynamic data compression. The so-called FAN, voltage triggered, two point projection and second difference methods. The comparison between the methods is based on 65 pressure, 46 uroflow and 18 surface electromyogram signals. The reduction ratio achieved for different allowable errors between the original and compressed signals is calculated and compared for the different techniques. Results show that it is possible to store urodynamic signals accurately at a low sampling rate, where FAN and voltage triggered methods seem to be superior to the rest.     

A heuristic for software evaluation and selection

The proliferation of software packages has created a difficult, complex problem of evaluation and selection for many users. Traditional approaches to the quantification of package performance have relied on compensatory models, such as the linear weighted attribute model, which sums the weighted ratings of software attributes. These approaches define the dimensions of quality too narrowly and, therefore, omit substantial amounts of information from consideration. This paper presents an alternative methodology, previously used in capital rationing and tournament ranking, that expands the opportunity for objective insight into software quality. In particular, it considers three measures of quality, the frequency with which the attribute ratings of one package exceed those of another, the presence of outliers, where very poor performance may exist on a single attribute and be glossed over by compensatory methods, and the cumulative magnitude of attribute ratings on one package that exceed those on others. The proposed methodology is applied to the evaluation of the following software types: word processing, database management systems, spreadsheet/financial planning, integrated software, graphics, data communications and project management.     

A High-Voltage Isolator for Conductive Liquids

In certain manufacturing operations, and particularly in electrostatic spray-coating, portions of a conductive liquid line may be exposed to a high potential. To localize the high potential, a new isolation system has been developed that allows the continuity of the conductive liquid to be broken and insulated by a gas medium. Experiments show that potential differences up to 100 kV may be successfully isolated over a distance of 10 cm.