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Biomedical subjects

R Williamson

Publications and source records attributed to R Williamson.

At least 433 records · Page 24Linked to original sources
PubMed1982

The purification of human DNA fragments containing benzpyrene adducts.

DNA was isolated from human diploid lung epithelial cells treated in culture with [3H]benzpyrene. The DNA contained one covalently bound benzpyrene group per 38 kb and it was digested with a series of restriction endonucleases giving decreasing fragment sizes, and also with DNAase I to 96% acid solubility. The digests were applied to octyl-Sepharose columns under conditions which promote hydrophobic interaction of the benzpyrene groups on the DNA with the octyl groups in the column matrix. Separation of fragments without and with benzpyrene groups was achieved with successive high salt and ethanediol washes. As DNA fragment size is decreased, more DNA-associated benzpyrene is eluted with ethanediol. Under these conditions, DNA from untreated cells is totally removed in the high salt wash and free benzpyrene metabolites are retained on the column. The separation of DNA fragments with covalently-bound hydrophobic benzpyrene groups, from less modified or unmodified DNA will facilitate examination of the distribution of benzpyrene adducts in defined regions of the human genome.

Animals↗
PubMed1982

The Mendelian inheritance of a human X chromosome-specific DNA sequence polymorphism and its use in linkage studies of genetic disease.

A recombinant DNA sequence, lambda RB6, was isolated from a human X chromosome library and shown to be X-specific by hybridisation to DNA from a human-mouse somatic cell hybrid containing X as the only human chromosome. The cloned sequence was located on the long arm distal to Xq13 using a human-mouse somatic cell hybrid containing a partial human X chromosome. DNA samples isolated from control human females were digested with the restriction enzyme MspI, and analysed by "blotting" and hybridisation to the radioactive cloned DNA. Eight of 14 individuals from a random population showed a single hybridising band 7.5 kilobase pairs (kb) in length, but six showed an additional band 10.1 kb in length. DNA from 12 members of a family with X-linked thyroxine-binding globulin deficiency was analysed for the segregation of this polymorphism. The results show that the polymorphism is inherited in a Mendelian fashion, and that the disease locus is not closely linked to the polymorphic site. Such polymorphisms will be useful as markers for chromosome mapping and for the antenatal diagnosis of genetic diseases.

Animals↗
PubMed1982

Benzylpenicillin-induced filament formation of Clostridium perfringens.

Growth of Clostridium perfringens with low concentrations of benzylpenicillin inhibited septum formation and division of the organisms. This resulted in continued growth of the organisms as aseptate filaments. The effect was reversed on removal of the antibiotic. The composition of walls isolated from organisms grown with the antibiotic was similar to that of walls from untreated bacteria. In addition, both contained non-N-acetylated glucosamine residues in their peptidoglycan. No differences were detected in the degree of cross-linkage of peptidoglycan. Clostridium perfringens contains six membrane-associated penicillin-binding proteins (PBPs) which have different affinities for [3H]benzylpenicillin. Concentrations of the antibiotic which were sufficient to cause filamentation of apparently all organisms in a culture caused almost complete saturation of PBPs 3, 4, 5 and 6. At these concentrations there was no measurable interaction with PBPs 1 and 2. Thus interaction of the antibiotic with the lower molecular weight PBPs is correlated with the inhibition of septum formation in C. perfringens.

Bacterial Proteins↗
PubMed1981

There are approximately 20 actin gene in the human genome.

By three different lines of evidence there are approximately 20 copies of actin genes in the human genome. Firstly, the rate of hybridisation of a mouse actin probe to human DNA indicates that there are a minimum of 20 complementary copies of the actin sequence per genome. Secondly, this probe hybridises to 17-20 bands in Southern blots of restriction enzyme digests of total human DNA. Most of these bands hybridise with both 3' and 5' fragments of the cDNA and are therefore likely to contain the entire gene sequence. Thirdly, we have picked 12 actin recombinants from a genomic library, and at the level of restriction enzymes mapping these represent nine different genes. Probability calculations indicate that these recombinants were picked from a pool of at least 20 different genes.

Actins↗
PubMed1981

Cloning of a representative genomic library of the human X chromosome after sorting by flow cytometry.

A library of 50,000 recombinants representative of the human X chromosome has been constructed. Human X chromosomes were physically separated using a fluorescence-activated cell sorter. The DNA was purified from the chromosomes, digested to completion with the restriction enzyme EcoRI and cloned into the phage lambda gtWES.lambda B. The X-derived nature of the recombinants was confirmed by hybridization to rodent/human cell line DNA containing only the human X chromosome. Such libraries will be particularly useful for the investigation of genetic diseases such as Duchenne muscular dystrophy, where the basic defect has not been elucidated, and of neoplasia, where several specific chromosomal anomalies, particularly for the leukaemias, have been identified.

Bacteriophage lambda↗
PubMed1981

An intron nucleotide sequence variant in a cloned beta +-thalassaemia globin gene.

A 7.5 kb Hsu I restriction fragment of genomic DNA containing a beta-globin gene has been isolated from a patient doubly heterozygous for beta + thalassaemia and a delta beta (Lepore globin fusion gene. This fragment must be derived from the chromosome carrying the beta +-thalassaemia determinant. The gross structure of the cloned gene plus flanking sequences is indistinguishable from that of a normal beta-globin gene. Within in 1606 base-pair transcribed region of the gene there is only one nucleotide difference from the normal beta-globin gene sequence. This is a G leads to A replacement 21 nucleotides upstream from the 3' terminus of the small intron. This nucleotide lies within a 10 base-pair sequence repeated in an inverted configuration near the 5' terminus of the small intron. The nucleotide replacement may result in a precursor mRNA less amenable to RNA splicing than its normal counterpart.

Adult↗
PubMed1981

Prenatal diagnosis of neural tube defects: predictive value of AF-AFP in a low-risk population.

Amniotic fluid alpha-fetoprotein (AF-AFP) determinations were performed on 1,215 women who were at low risk for fetal neural tube defects and who were undergoing mid-trimester amniocentesis for cytogenetic indications, primarily age-related aneuploidy. Maternal sera obtained before amniocentesis and amniotic fluids were assayed in duplicate for alpha-fetoprotein by radioimmunoassay. Of the 1,215 low-risk women, eight (0.7%) had significant elevations of AF-AFP (greater than or equal to +5 SD). In none of the cases was the elevation associated with a fetal neural tube defect. Two cases with elevated AF-AFP were associated with chromosome aberrations; one with impending fetal demise; one with fetal blood contamination; and one case was due to a laboratory error. In one case, no source for the elevated AFP was found, and a normal infant was delivered at term. In the final two cases, the cause of the elevated AF-AFP was a fetal abdominal wall defect (one gastroschisis and one omphalocele). The predictive value of an elevated AFP varies with the population screened, and is reduced by routine ultrasonography before amniocentesis, which at least identifies anencephaly. In a low-risk population, an elevated AF-AFP is most often not associated with a fetal neural tube defect. Because of the low predictive value and the nonspecificity of AF-AFP, genetic counselors should reconsider the recommendation of routine AF-AFP in low-risk maternal populations.

Amniocentesis↗
PubMed1981

Method for calculating blood loss at vaginal delivery.

We describe a method for calculating blood loss at vaginal delivery using a special plastic drape. Blood loss is calculated from the sum of three components: (1) blood lost in sponges, (2) blood loss represented by clots, and (3) blood loss represented by unclotted RBC. The procedure has been used in ten patients and the results are presented. The obstetrician would know the maximal potential blood loss immediately after delivery. If this figure is less than 15% of the estimated blood volume, further calculation might be deemed unnecessary. If this figure exceeds 15% of the estimated blood volume, however, the full procedure described should be done. The final result could be available to the obstetrician within approximately four hours after delivery.

Blood Volume↗
PubMed1981

Deficiency of autolytic activity in Bacillus subtilis and Streptococcus pneumoniae is associated with a decreased permeability of the wall.

Autolytic-deficient mutants of Bacillus subtilis which grow as chains of non-separated bacilli have been isolated by a procedure involving filtration of mutagenized cultures through glass-sinter filters. The mutants obtained were some 80-90% deficient in both autolysins, N-acetylmuramoyl-L-alanine amidase and endo-beta-N-acetylglucosaminidase. Treatment of one of these mutants with 5 M-LiCl extracted only about 20% of the protein obtained from an equivalent amount of the autolysin-containing bacilli. Similarly, a reduction of 40-60% in LiCl-extractable protein was obtained with autolytic-deficient Streptococcus pneumoniae whether these organisms lacked the autolytic enzyme or were phenotypically deficient by growth in ethanolamine-containing medium. Chromatography on Sephadex G-100 of the protein extracted from B. subtilis and S. pneumoniae revealed that the major difference between autolytic-deficient and parent organisms was a decrease in proteins of high molecular weight. Smaller differences were observed in a second fraction which contained low molecular weight material and proteins such as the autolysins, whose elution from the column was retarded by interaction with the Sephadex. Further examination of the fractionated protein from B subtilis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis confirmed that the major difference between the extracts was in the amount of protein present and did not result from marked changes in the size of the extracted proteins. These observations suggest that autolysin deficiency in B. subtilis and S. pneumoniae results in a change in the porosity (permeability) of the bacterial wall.

Acetylglucosaminidase↗
PubMed1981

The isolation, mapping and transcription in vitro of a beta 0-thalassaemia globin gene.

The red blood cell precursors of a patient with homozygous beta 0-thalassaemia have previously been shown to contain nuclear, but not cytoplasmic, beta-globin-specific transcripts. We describe the isolation of a beta-globin gene from this patient as a recombinant bacteriophage chromosome. Restriction-enzyme cleavage-site mapping experiments demonstrate no detectable deletions, insertions or major rearrangements in this thalassaemia gene. Two different techniques show that the gene isolated is transcribed as efficiently in vitro as the normal beta-globin gene.

Base Sequence↗
PubMed1981

Physiological properties of penicillin-binding proteins in group A streptococci.

We detected five major penicillin-binding proteins (PBPs) in group A streptococci by labeling either cell membrane preparations or live bacteria with tritiated penicillin. All PBPs appeared to be equally accessible to penicillin in vitro and in vivo. Individual PBPs differed in their rates of deacylation, and four of the five PBPs underwent rapid inactivation both in vivo and in vitro. At least two processes seemed to contribute to in vivo inactivation; these were (i) a penicillin-induced release of all five PBPs into the growth medium and (ii) degradation, as evidenced by the appearance of penicillin-labeled protein band of lower molecular weight and also by a gradual increase in material migrating with the same electrophoretic mobility as PBP 3. Inactivation of the PBPs was stimulated greatly by pretreatment of bacteria with gentamicin, cerulenin, or Triton X-100, whereas chloramphenicol, tetracycline, and lincomycin treatments had no such effect.

Anti-Bacterial Agents↗
PubMed1980

The isolation of cloned cDNA sequences which are differentially expressed in human lymphocytes and fibroblasts.

Poly(A)+ RNA populations derived from normal lymphocytes and fibroblasts have been compared by hybridising each RNA to cDNA derived from the other RNA population. This indicated that approximately 75% of the sequences were common to both, and that these were present at different concentrations in the two cell types. The two RNA populations were further compared by hybridising them to a cDNA recombinant library derived from lymphocyte poly(A)+ RNA. This allowed the identification of clones containing sequences which are abundant in lymphocyte poly(A)+ RNA but absent or rare in fibroblast poly(A)+ RNA. A direct estimation of the abundance of five of these sequences in lymphocyte cDNA demonstrated that clones can be detected by such a procedure if they represent 0.2% or greater of the original cDNA population.

Animals↗
PubMed1980

The construction of a recombinant cDNA library representative of the poly(A)+ mRNA population from normal human lymphocytes.

A recombinant library has been constructed using the plasmid pAT153 and double stranded cDNA prepared from normal human lymphocyte poly(A)+ RNA. Transformation conditions were optimized to yield approximately 200,000 recombinants per microgram of double stranded cDNA. Statistical analysis as well as sequence complexity analysis of the inserted sequences indicates that the cDNA library is representative of > 99% of the poly(A)+ RNA present in the normal human lymphocyte.

Base Sequence↗