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R Williamson

Publications and source records attributed to R Williamson.

At least 343 records · Page 19Linked to original sources
PubMed1987

Exclusion of catalytic and regulatory subunits of cAMP-dependent protein kinase as candidate genes for the defect causing cystic fibrosis.

Cystic fibrosis (CF) is a common autosomal recessive disease with significant morbidity and mortality. Defects in cAMP control mechanisms are implicated in the pathophysiology of the disease. The mutation causing CF has been localized to chromosome 7q22-7q31.1. We have used (1) somatic-cell hybrids containing this region of the human genome in a mouse background and (2) segregation analysis in families to exclude both the genes coding for a catalytic subunit and three distinct regulatory subunits of cAMP-dependent protein kinase as candidates for the gene defect in CF. Two of these genes--those for the human homologue of the mouse type I regulatory subunit and the human homologue of the rat type II regulatory subunit--map to human chromosome 7.

Animals↗
PubMed1986

[Mechanisms of action of beta-lactam antibiotics and mechanisms of non-enzymatic resistance].

The mode of action of beta-lactam antibiotics, and the non-enzymatic resistance mechanisms to their activity, are intimately linked to the structure and biosynthesis of the bacterial cell wall. The bacteriostatic effect of beta-lactam antibiotics is related to their various interactions and concomitant inhibition of essential enzymes (transpeptidases, carboxypeptidases) involved in the terminal stages of peptidoglycan biosynthesis. These cytoplasmic membrane-associated target enzymes bind the antibiotics covalently, and hence are known as penicillin-binding proteins (PBPs). The bactericidal effect of these antibiotics is due to a second step following on from the inhibition of cell division and growth, in which the activation of an autolytic system causes cell death. Resistance to beta-lactam antibiotics in Gram-positive bacteria, in the absence of a beta-lactamase, is due to various modifications of the PBPs. Such mechanisms are often found in enterococci, pneumococcus, ans staphylococci. With Gram-negative bacteria such modifications of PBPs are only a rare basis for resistance. The presence of an outer membrane brings another factor into the activity of beta-lactam antibiotics, which is the facility with the antibiotics can diffuse through specialised proteins termed porins. It is generally a modification of the amounts of these proteins, or some other components of the outer membrane, which causes the non-enzymatic mechanism of resistance, particularly in species such as Klebsiella, Enterobacter, Serratia and Pseudomonas.

Anti-Bacterial Agents↗
PubMed1986

Genetic homogeneity of cystic fibrosis.

We studied large Amish/Mennonite/Hutterite kindreds that segregate cystic fibrosis (CF) for linkage between CF and the polymorphic DNA markers pJ3.11 and 7C22 located on chromosome 7. These inbred pedigrees consist of more than 300 members including 30 affected individuals. In these families, linkage between the CF locus and the chromosome 21 marker D21S5 and between CF and the marker at the met oncogene locus on chromosome 7 had been previously indicated. We now report linkage between CF and pJ3.11 (Z = 4.92, theta = 0) and between CF and 7C22 (Z = 3.42, theta = 0). Therefore, CF segregates in these large pedigrees in a manner consistent with data from smaller outbred families with respect to the markers on chromosome 7 closest to CF. These data are consistent with locus homogeneity for the defect causing CF in the populations that have been examined to date.

Chromosomes, Human, Pair 21↗
PubMed1986

Chromosome mediated gene transfer of six DNA markers linked to the cystic fibrosis locus on human chromosome seven.

The DNA probes met and pJ3.11 are derived from loci on chromosome seven that are closely linked to, and probably flanking, the gene mutation causing cystic fibrosis (CF). We have shown that mitotic chromosomes from the cell line MNNG-HOS, which contains an activated met oncogene, can induce morphological transformation of mouse NIH-3T3 cells. Southern analysis of isolated transfectant cell lines with cloned dispersed repetitive human DNA sequences as probes demonstrated that several lines of transformed NIH 3T3 cells had stabley incorporated large segments of chromosome seven DNA. Southern blot analysis also demonstrated the presence of met, pJ3.11 and several other single copy sequences that had been previously localised to chromosome 7 within the transgenomes. In this way a further four genetic markers were shown to be physically linked to met, and thus to CF. These probes may prove useful in confirming the order of loci around CF and in the prenatal diagnosis of this common autosomal recessive disease.

Animals↗
PubMed1986

A quantitative analysis of the spinal motor pool and its target muscle during growth in the dogfish, Scyliorhinus canicula.

In order to relate the phenomenon of continuous growth in fishes to the development of the neuromuscular system, we established the numbers and sizes of spinal motoneurons and red and white axial muscle fibers in late- and post-embryonic dogfish within the size range 6-71 cm. We found that motoneuron somata, ventral root axons, and red and white muscle fibers increase their size throughout the life of the animal; there is an initial increase in the number of motoneurons that ceases as the fish reaches a length of about 40 cm; white muscle fibers initially decrease in number during post-embryonic life; and red muscle fibers increase in number, but this increase levels off at a fish length of about 40 cm. Spinal motoneurons innervating red myotomal muscle fibers or centrally located white muscle fibers were identified after retrograde labeling with horseradish peroxidase, which was injected in small amounts into the respective muscle areas. The motoneurons supplying the red muscle are smaller and occupy a more lateral position in the ventral horn than the white muscle motoneurons. The number of motoneurons in the ventral horn per unit area increases from medial to lateral and this is associated with a reduction in the sizes of the somata. Values for the ratio of number of muscle fibers to number of supplying motoneurons in the various muscle areas were based on axon counts within the peripheral nerves. This ratio was higher for the centrally located white muscle fibers than for the ventral or dorsal white fibers, but was highest for the red fibers.

Animals↗
PubMed1986

Synergism and antagonism in double beta-lactam antibiotic combinations.

Combinations of two beta-lactam antibiotics may be advantageous in certain clinical situations, providing a synergistic activity against specific organisms or a broad spectrum of antibiotic coverage. Depending on the combination and the bacteria, synergism, indifference, or antagonism can be observed. Synergism may occur when two beta-lactam antibiotics, acting on different penicillin-binding proteins, are combined or when a penicillinase-susceptible beta-lactam antibiotic is protected by another beta-lactam antibiotic acting as a beta-lactamase inhibitor in strains producing a penicillinase (chromosomal or plasmidic). With different species, such as Enterobacter, Citrobacter, indole-positive Proteus, Serratia, Aeromonas, and Pseudomonas, which produce an inducible chromosome-encoded cephalosporinase, antagonism will appear if one of the two combined antibiotics causes induction of the beta-lactamase and the other becomes inactivated by the increased amount of the enzyme. Although most combinations of new beta-lactam antibiotics (ureido-penicillins, third-generation cephalosporins, monobactams) appear to be indifferent, antagonism and possible selection of resistant mutants are the drawbacks of such combinations. Nevertheless, highly active compounds, if used at doses above the minimal inhibitory concentrations, especially in the case of potential cephalosporinase-inducers, may be safe in vivo as far as avoiding antagonism is concerned, but not necessarily with respect to the selection of resistant mutants.

Anti-Bacterial Agents↗
PubMed1986

There are two gene sequences for human apolipoprotein CI (apo CI) on chromosome 19, one of which is 4 kb from the gene for apo E.

A cDNA probe corresponding to the mRNA sequence for apolipoprotein E (apo E) was used to screen two independently-constructed human genomic libraries. Two recombinants (lambda E-2, and lambda E2-1), isolated using the apo E cDNA probe, also contain part or all of the apo CI gene. Hybridisation studies using both apo E and apo CI cDNA probes show that these two genes are in the same orientation and separated by 4 kb.

Apolipoprotein C-I↗
PubMed1986

Isolation of a further anonymous informative DNA sequence from chromosome seven closely linked to cystic fibrosis.

A library prepared from flow-sorted chromosomes was used to isolate single-copy sequences from chromosome seven. One such sequence 7C22 has been shown to be polymorphic for an EcoRI restriction site and to be informative for the study of CF in approximately 35% of matings. The segregation of the 7C22 alleles was followed through nineteen informative families with more than one child affected by cystic fibrosis. We report that the locus for 7C22 is linked to the locus for cystic fibrosis at a recombination fraction of 0.045. This marker will prove useful in improving the accuracy and informativeness of prenatal diagnosis and in constructing a fine genetic map around the cystic fibrosis gene.

Chromosomes, Human, 6-12 and X↗
PubMed1986

Chromosome assignment and restriction fragment length polymorphism analysis of the anonymous DNA probe B79a at 7q22 (HMG8 assignment D7S13).

The anonymous DNA fragment B79a, which had previously been located to chromosome 7cen-7q22, has been more accurately assigned to 7q22 by dosage analysis in a patient hemizygous for a deletion of that region. By examination of a panel of genomic DNAs from unrelated individuals, digested with a number of different restriction enzymes, we have identified two frequent RFLPs detected by B79a. This probe will be important in the analysis of cystic fibrosis which has been mapped to the region around 7q22.

Chromosome Mapping↗
PubMed1986

Cloning of Drosophila choline acetyltransferase cDNA.

Choline acetyltransferase (EC 2.3.1.6) is the biosynthetic enzyme for the neurotransmitter acetylcholine. To isolate choline acetyltransferase cDNA clones, a cDNA library was constructed from poly(A)+ RNA of Drosophila melanogaster heads, these being one of the richest known sources of the enzyme. By screening the cDNA library with a mixture of three different monoclonal antibodies to Drosophila choline acetyltransferase, we isolated 14 positive clones. Only 1 of these clones was identified to be a Drosophila choline acetyltransferase cDNA clone based on the following evidence. (i) The amino acid sequence deduced from the nucleotide sequence of the cDNA insert completely corresponded to that of several tryptic peptides from choline acetyltransferase. (ii) The cDNA insert hybridized specifically to only the region on Drosophila polytene chromosomes that had been identified as the site of the choline acetyltransferase (Cha) gene by cytogenetic analysis. The cDNA insert consisted of a coding region 2190 nucleotides long, a 3'-noncoding region 284 nucleotides long, and EcoRI linkers. RNA analysis of Drosophila head poly(A)+ RNA with the cDNA insert as a probe showed the choline acetyltransferase mRNA to be approximately equal to 4700 nucleotides long.

Amino Acid Sequence↗
PubMed1986

Use of penicillin-binding proteins for the identification of enterococci.

The results of 20 physiological and fermentation tests and examination of the penicillin-binding proteins (PBPs) of 85 enterococcal strains demonstrated that the genus Enterococcus could be divided into at least nine distinct species: E. faecalis, E. faecium, E. durans, E. hirae, E. avium, E. gallinarum, E. casseliflavus, E. malodoratus and E. mundtii. Each species had a specific pattern of at least five PBPs, with molecular masses in the range of about 40-130 kDa. The pattern of PBPs may be useful for identification purposes, since some strains with unusual fermentation characteristics were assigned to species by this technique.

Bacterial Proteins↗
PubMed1986

Linkage between the loci for cystic fibrosis and paraoxonase.

In a material of 22 Danish, 26 Canadian, 10 Australian, 5 English and 5 American families with at least 2 children affected with cystic fibrosis (CF) a combined positive LOD score of 3.46 was found for the relationship cystic fibrosis-paraoxonase (PON) at recombination fraction theta = 0.07 in males and theta = 0.13 in females. Assuming a three allele model for PON the LOD score was 4.50 at the same recombination fractions. This confirms our earlier finding of an indication of CF-PON synteny.

Alleles↗
PubMed1986

Involvement of penicillin-binding protein 2 with other penicillin-binding proteins in lysis of Escherichia coli by some beta-lactam antibiotics alone and in synergistic lytic effect of amdinocillin (mecillinam).

Compared with cefotaxime, ceftazidime, moxalactam, and aztreonam, ceftriaxone produced the best lytic and bactericidal effects when each was added at about 10 times the MIC to Escherichia coli W7. When each of these antibiotics was added at its MIC, only bacteriostasis occurred, but the simultaneous addition of amdinocillin (mecillinam) was synergistic in causing rapid lysis and bactericidal effects. Induction of lysis of two E. coli mutants containing either a thermosensitive penicillin-binding protein (PBP) 2 or 3 by relatively PBP 3-specific (aztreonam) and PBP 2-specific (amdinocillin) antibiotics indicated that inhibition of only PBPs 2 and 3 can cause lysis. Examination of the interactions of cefotaxime, aztreonam, and cefsulodin, with or without amdinocillin, with their targets suggested that other combinations of PBPs could be involved in the onset of lysis. However, inhibition of both PBPs 2 and 3 may explain the better lysis-inducing activity of ceftriaxone (which binds well to both of these PBPs), as well as the synergistic effect of amdinocillin when added together with low concentrations of other beta-lactam antibiotics that interact with PBP 3.

Acyltransferases↗