Biomedical subjects
Publications and source records attributed to M Williamson.
A 1.3-kb cDNA that encodes the entire 825-bp coding region of ovine CD25, the interleukin-2 receptor 55-kDa protein, has been isolated. Comparison of the deduced amino acid sequence with CD25 proteins from other species shows the ovine sequence to have the greatest homology with that of the bovine species.
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The crystal structure of Cd5,Zn2-metallothionein from rat liver has been refined at 2.0 A resolution of a R-value of 0.176 for all observed data. The five Cd positions in the asymmetric unit of the crystal create a pseudo-centrosymmetric constellation about a crystallographic 2-fold axis. Consequently, the distribution of anomalous differences is almost ideally centrosymmetric. Therefore, the previously reported metal positions and the protein model derived therefrom are incorrect. Direct methods were applied to the protein amplitudes to locate the Cd positions. The new positions were used to calculate a new electron density map based on the Cd anomalous scattering and partial structure to model the metal clusters and the protein. Phases calculated from this model predict the positions of three sites in a (NH4)2WS4 derivative. Single isomorphous replacement phases calculated with these tungsten sites confirm the positions of the Cd sites from the new direct methods calculations. The refined metallothionein structure has a root-mean-square deviation of 0.016 A from ideality of bonds and normal stereochemistry of phi, phi and chi torsion angles. The metallothionein crystal structure is in agreement with the structures for the alpha and beta domains in solution derived by nuclear magnetic resonance methods. The overall chain folds and all metal to cysteine bonds are the same in the two structure determinations. The handedness of a short helix in the alpha-domain (residues 41 to 45) is the same in both structures. The crystal structure provides information concerning the metal cluster geometry and cysteine solvent accessibility and side-chain stereochemistry. Short cysteine peptide sequences repeated in the structure adopt restricted conformations which favor the formation of amide to sulfur hydrogen bonds. The crystal packing reveals intimate association of molecules about the diagonal 2-fold axes and trapped ions of crystallization (modeled as phosphate and sodium). Variation in the chemical and structural environments of the metal sites is in accord with data for metal exchange reactions in metallothioneins.
The use of optimally methylation-tolerant mcrA- mcrB- strains has been shown to produce an over tenfold increase in the plating efficiencies of mammalian genomic libraries, compared to a superior conventional phage host strain LE392 which is mcrB+. However, there is an even more significant effect of mcr restriction. Amongst the recombinants recovered with an mcrB+ host, we have found that there is an additional 30-fold reduction in the frequencies of clones containing the heavily methylated 5'-CpG island sequences of both the human and rat L1 repetitive elements. The mcrA product was also found to restrict clones of these methylated genomic segments, but not as strongly as mcrB. However, the use of packaging extracts made from mcrA+ lysogens did not result in convincing reductions in the recoveries of these dispersed methylated elements. The magnitude of mcr restriction during plating due to methylated dispersed elements is sufficient to make a significant proportion of mammalian genomes unclonable from genomic libraries constructed previously using conventional mcr+ hosts.
A working prototype database of authoring system software was developed as part of a study of authoring software conducted by the National Library of Medicine. The database and development issues ranging from the scope of the database to what information to document are described. The protype demonstrates that records of reasonable integrity can be derived from vendor supplied information as long as users understand the database is only an initial starting point in searching for authoring software and a resource for becoming generally familiar with the technology.
The presence of multiple heterologies in a 9-kilobase (kb) interval results in a decrease in meiotic crossovers from 26.0% to 10.1%. There is also an increase from 3.5% to 11.1% in gene conversions and ectopic recombinations between the flanking homologous MAT loci. The hypothesis that mismatch repair of heteroduplex DNA containing several heterologies would lead to a second round of recombination has now been tested by examining the effect of a mutation that reduces mismatch correction. The repair-defective pms1-1 allele restores the pattern of recombination to nearly that seen in congenic diploids without the heterologies. Mismatch repair-induced recombination causes a significant increase in MAT conversions and ectopic recombination events with as few as two heterozygosities separated by 0.3-0.7 kb, but not when the mismatches are separated by greater than 1 kb. The frequency of these events depends on both the number and position of the heterozygosities relative to the flanking homologous MAT loci used to detect the events. The creation of recombinogenic lesions by mismatch repair in yeast could be analogous to the creation of recombinogenic lesions in dam- Escherichia coli. We suggest that the repair of heteroduplex DNA containing multiple mismatches may produce chromosomal rearrangements and gamete inviability when naturally polymorphic chromosomes undergo meiotic recombination.
There was an increase in incidence of meningitis in children within the last three years at the Bai Yamunabai Laxman Rao Nair Charitable Hospital in Bombay. Out of 270 purulent samples, 60 (22.22 percent) were culture positive. Neisseria meningitidis showed an increase from one case in 1985 to 11 cases by the end of 1987. Staphylococcus aureus was isolated from 6 percent cases, Streptococcus pneumoniae 15 percent, and Gram negative bacilli were predominant, isolation rate being 57 percent. Salmonella species were isolated from 6 (10 percent) cases. They were multidrug resistant type, some belonging to the rare zoonotic species.
Almost all recent extinction of species or subspecies on islands comes from human activities. On the other hand, in local populations there is much natural extinction and immigration, i.e. turnover, on small islands. Most of this turnover occurs in locally rare species, and attests to the phenomenon of minimum viable population size. The MacArthur-Wilson theory is based on this turnover which, from an ecological point of view, is generally trivial. More useful theories of minimum viable population size are being developed. Rarity is the precursor of extinction, and species can be rare in several ways. Models of these phenomena are still primitive, particularly those that relate habitat availability to population density. Models of interactive communities show phenomena that may be relevant to the understanding of extinction in the geological record. Lotka-Volterra equations indicate considerable sensitivity to invasions, sometimes producing a cascade of extinction. Chemostat equations show that the behaviour of food chains can change dramatically with small changes in parameters, suggesting that small environmental effects can sometimes cause large ecological changes, including extinctions, in interactive biotic communities.
31P nuclear magnetic resonance spectroscopy was used to measure the pKa (4.28 +/- 0.2) of isophosphoramide mustard (IPM) at 20 degrees C and to study the kinetics and products of the decomposition of IPM at a solution pH value of ca. 7.4 and at temperatures between 20 and 47 degrees C in the presence of nucleophilic trapping agents. At 37 degrees C, the half-life for the first alkylation was ca. 77 min and ca. 171 min for the second alkylation; these data may be compared with those for phosphoramide mustard (Engle, T.W.; Zon, G.; Egan, W.J. Med. Chem. 1982, 25, 1347), wherein the half-lives for the first and second alkylations are approximately the same (18 min). The rate of fragmentation of aldoifosfamide to IPM and acrolein was also studied by NMR spectroscopy (pH 7.0; 37 degrees C; 0.07 M phosphate); under the noted conditions, the half-life of aldoifosfamide was found to be ca. 60 min.
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The primary structure of barley endosperm beta-amylase, an enzyme which catalyses the liberation of maltose from 1,4-alpha-D-glucans, has been deduced from the nucleotide sequence of a cloned full-length cDNA. The mRNA is 1754 nucleotides long [excluding the poly(A) tail] and codes for a polypeptide of 535 amino acids with a relative molecular mass of 59,663. The deduced amino acid sequence was compared with the sequences of ten peptides obtained from the purified enzyme and unambiguous identification was obtained. The N-terminal region of the deduced sequence was identical to a 12-residue cyanogen-bromide-peptide sequence, indicating that beta-amylase is synthesized as the mature protein. A graphic matrix homology plot shows four glycine-rich repeats, each of 11 residues, preceding the C-terminus. Southern blotting of genomic DNA demonstrates that beta-amylase is encoded by a small gene family, while cDNA sequence analysis indicates the presence of at least two types of mRNA in the endosperm. Dot and northern blot analysis show that Hiproly barley contains greatly increased levels of beta-amylase mRNA compared to the normal cultivar Sundance, whereas Risø mutant 1508 contains only trace amounts. These results correlate well with the deposition of beta-amylase during endosperm development in these lines. Low but similar amounts of beta-amylase mRNAs sequences were detected in leaves and shoots from normal and mutant barleys, demonstrating that the mutant lys3a (1508) and lysl (Hiproly) genes do not affect the expression of beta-amylase in these tissues.
Height, weight, and head circumference data up to age 4 years are reported for 124 children with phenylketonuria (PKU) who had been started on diet management before 4 months (121 days) of age and who were participating in the Collaborative Study of Children Treated for Phenylketonuria. Growth measurements of both the children and their parents corresponded with national and international standards. The growth of children with PKU was compared also with that of a group of normal children in the United States in whom corresponding longitudinal growth data had been obtained at the Fels Research Institute (FRI). Statistically significant differences betweeen the groups were not noted at any age. However, when these groups were compared on coefficients using curve fitting, a trend toward a greater increase in weight as they became older, noted in both sexes in the PKU study group, was significantly higher (P less than .005) in the PKU study girls compared with the FRI sample. Height growth was identical in both groups, and comparison with family data showed that the children with PKU grew as expected for their genetic endowment.
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Better problem identification and improved access to community health care were the result of changes made during the past three years in a traditional urban high school health service. The first change included training the nurse to become a pediatric nurse practitioner and adding a full-time health aide. The other change included the use of clinic management forms developed by the nurse practitioner/health aide team to be used for three common student complaints: headache, stomachach and upper respiratory symptoms. Our experience indicates that out-of-school referrals for medical care doubled, and more students referred received care after these changes were instituted. The high school pediatric nurse practitioner counsels students in understanding their health problems and in making decisions about their health care. She also coordinates educational and health resources and provides psychosocial support for students.
Information on methods of initiating the phenylalanine-restricted diet was obtained from the medical personnel of sixteen clinics in the Collaborative Study of Children Treated for Phenylketonuria. The four dietary methods used initially to lower serum phenylalanine were: Normal dilution Lofenalac, Lofenalac, with phenylalanine added as milk, Lofenalac with milk added to provide 200 mg. phenylalanine per day, and alternating bottles of normal dilution Lofenalac and cow's milk during the first four days of therapy. During the first week of treatment, eight clinics obtained serum phenylalanine determinations daily or every other day. The nutritionist prescribed the phenylalanine-restricted diet following diagnosis in nine of the clinics. In most clinics, the nutritionist was responsible for obtaining information relating to dietary management and follow-up contacts during the first month of treatment. The initial dietary instruction was accomplished in most clinics by a combination of lecture/discussion/demonstration methods. Both parents attended the initial dietary instruction in thirteen clinics. Neither the professional person(s) nor the method of initial dietary instruction, if detailed and comprehensive, made any difference in control of serum phenylalanine during the first year of life.
Growth, energy, and nutrient intake of 88 treated infants in the Collaborative Study of Children Treated for Phenylketonuria were evaluated longitudinally and compared to normative data and by treatment group. Growth parameters (height and weight) did not differ according to treatment group assignment, nor did they differ from normative data. Subjects in treatment group 2 had a significantly higher intake of phenylalanine than did subjects in treatment group 1. Differences in intake of other nutrients disappeared when intake was compared on an energy or body weight basis. Differences in intake by males and females also disappeared when compared on an energy and a body weight basis. From none to 10% of the subjects had energy intakes below two-thirds of the 1968 Recommended Dietary Allowances (RDA). Low individual energy intakes were more commonly found in the first and fourth quarters, and only during the first quarter of infancy did mean energy intake meet the RDA. From 48 to 80% of subjects had intakes of preformed niacin below two-thirds of the 1968 RDA. Few subjects had low intakes of protein, iron, or vitamin A, and intakes of all subjects were greater than 67% of the RDA for calcium, phosphorus, thiamin, riboflavin, and ascorbic acid. It is suggested from the data presented that a supplemental casein hydrolysate supplies adequate essential amino acids and nitrogen to support normal growth in infants when protein and energy intakes are fed at the levels described.
Studies that have attempted to test the effectiveness of treatment in phenylketonuria (PKU) have been handicapped by small samples due to rarity of the disorder and inadequate control of other sources of error. The present study was designed to overcome these limitations by treating a large number of children with PKU under controlled conditions from near birth to 6 years of age. Nineteen medical centers in 13 states have participated in the study, which is currently in progress. This article is one of a series of final reports. It describes the study design and sampling procedures employed to answer questions of interest for which results will be reported in subsequent articles. The study serves as a model for future collaborative investigations of a similar nature.