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Biomedical subjects

L Duncan

Publications and source records attributed to L Duncan.

At least 73 records · Page 4Linked to original sources
PubMed1988

Heterologous 5' flanking regions do not support in vitro template activity of a Drosophila melanogaster tRNA(Val3b) gene.

The 5' and 3' structure of a Drosophila tRNA(Val3b) gene was investigated to examine the defect which caused the extremely low in vitro transcription template activity of the gene. Recombinant genes were constructed linking 5' and 3' flanking regions from tRNA genes which were active in vitro templates (tRNA(Val4), tRNA(Arg), tRNA(Ser7)) to the tRNA(Val3b) gene. None of the recombinant genes were effective in vitro templates. The defect in tRNA(Val3b) was demonstrated to reside in the 5' flanking region of the gene and deletion analysis indicated that no specific transcription inhibitor sequence was present 5' to the gene. The data suggest that the effect of 5' flanking sequences on in vitro transcription of the tRNA(Val3b) gene requires a specific relationship between the tRNA gene and the flanking sequence.

Animals↗
PubMed1988

Distinct epitopes recognized by I-Ad-restricted T-cell clones within antigenic site E on influenza virus hemagglutinin.

A total of 14 I-Ad-restricted helper T-cell clones specific for the hemagglutinin (HA) molecule of influenza virus were isolated from spleens of BALB/c or (BALB/c X C57BL/10)F1 mice immunized with the H3 subtype influenza virus A/Memphis/71 (Mem 71) and from lymph nodes of BALB/c mice primed with purified HA. The specificity of these T-cell clones was assessed in proliferation assays by reactivity with naturally occurring strains of viruses that arose by antigenic drift and contain known amino acid sequence changes in HA and with a panel of monoclonal antibody (MAb)-selected mutants of Mem 71 with single amino acid substitutions in HA. The HA genes of those mutant viruses that failed to stimulate one or more of the T-cell clones were sequenced. The clones could be allocated to at least four groups, each group having a distinct pattern of reactivity with the panel of natural field strains. The epitopes recognized by the four groups of clones were found, by reactivity with MAb-selected mutants, to be in very close proximity to one another and probably overlapping. All of the distinct epitopes recognized by the T-cell clones were adversely affected by a single amino acid substitution, either at residue 60 or at residue 63 in the HA1 polypeptide chain, within the region known from antibody-binding studies as site E. Some, but not all, of the epitopes may be influenced by the addition of a carbohydrate side chain to the HA of a particular MAb-selected mutant and certain field strains containing an Asp----Asn substitution at residue 63. Site E is therefore a major site of H-2d helper T-cell recognition on the H3 HA.

Amino Acid Sequence↗
PubMed1985

Partial purification of stable transcription complexes with cloned tRNA genes of Drosophila melanogaster.

The specific transcription of a cloned Drosophila melanogaster tRNAVal4 gene and a tRNASer7 gene by extracts from a homologous embryonic cell line showed lag periods of about 30 min before maximum rates were reached. This lag appeared to represent the time to form an active transcription complex. Thus, when extracts were incubated with template DNA for 30 min at 22 degrees C and stored in the cold, the subsequent transcription rate was linear with time and without a lag. After ultracentrifugation of a preincubated reaction mixture on a sucrose step gradient consisting of 20, 30, 40, and 60% shelves, about 40% of the transcription activity in the extract was found in the 40% shelf. This fraction formed almost exclusively RNA I, the unprocessed tRNA gene transcript, and transcription required only addition of ribonucleoside triphosphates. The rate of formation of RNA by the 40% sucrose fraction was linear against time, with no lag, and linear with the quantity of fraction. The yield of activity isolated on the gradient was directly proportional to the quantity of cloned gene in the preincubation mixture. At a limiting concentration of the gene in the preincubation mixture, the turnover number of the isolated complex was approximately 50 transcripts/gene/h. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of fractions containing the complex still showed many bands, although the complex activity was greatly purified compared to the extract. From the sedimentation behavior of the isolated active transcription complex and from its stability and transcriptional properties, we conclude that the 40% sucrose fraction contains an active transcription complex containing a cloned tRNA gene, RNA polymerase III, and the accessory protein factors required for transcription.

Animals↗
PubMed1983

Mitochondrial abnormalities in muscle from vitamin B12-deficient sheep.

Skeletal and cardiac muscles from vitamin B12-deficient sheep were examined. Histochemical studies did not reveal any gross pathological changes in the muscle structure, but there was an abnormal distribution of the product of the NADH-diaphorase reaction. Electron microscopy revealed an abnormal distribution of mitochondria, changes in the number and arrangement of cristae within the mitochondria and the presence of inclusions. The possibility that alterations in mitochondrial morphology are early lesions attributable to metabolic changes in vitamin B12 deficiency is discussed.

Animals↗
PubMed1983

Effect of zinc deficiency on muscle fibre type frequencies in the post-weanling rat.

Male weanling rats were maintained on diets either deficient or adequate in zinc for a period of 4 weeks. The rats on the deficient diet showed a reduction in food intakes and growth. After 4 weeks both soleus muscles and the lateral portion of the diaphragm were studied histochemically to examine the relative frequencies of the fibre types. The soleus muscles of the deficient animals showed a significant change in the proportion of slow and fast fibres. The diaphragm muscles of the deficient animals had a significant increase in the proportion of fast-twitch oxidative glycolytic fibres and a significant decrease in fast-twitch glycolytic fibres compared with the controls. Stainable lipid increased in the diaphragm muscle of the deficient animals with respect to their pair-fed controls.

Animals↗
PubMed1982

Transcription of cloned transfer RNA genes from Drosophila melanogaster in a homologous cell-free extract.

Cloned Drosophila melanogaster tRNA genes have been transcribed in a homologous cell-free extract isolated from a Schneider II cell line. The major product of the reaction is a tRNA precursor which is processed to a tRNA sized species. The kinetics of transcription has been followed for 5 different valine tRNA gene clones. The results demonstrate formation of stable transcription complex with at least two kinetic steps. While the rate of formation of the transcription complex is similar to different clones, the ultimate rate of transcription varies dramatically. Comparison of the DNA sequence of the tRNA genes suggests that rate determining nucleotides lie outside the canonical tRNA split-internal promoters.

Animals↗
PubMed1981

Inflatable bath for external cooling.

The authors describe an inflatable bath which can be used rapidly and safely, with a minimum of patient manipulation, for external cooling of hyperthermic patients or in the elective induction of hypothermia. This device permits ready access to the patient so that monitoring and treatment can be carried on while cooling is in progress and is particularly adopted to use in the operating room.

Anesthesiology↗
PubMedDate not supplied

Rat diaphragm: changes in muscle fiber type frequency with age.

This study demonstrates age-related changes in fiber type, distribution, and diameter that suggest that the diaphragm does not attain a static pattern of fiber type in adults. Furthermore, the progressive increase in the FG fiber diameters may be of importance in the interpretation of physiologic and biochemical parameters measured in the diaphragm muscle of animals of different age groups.

Adenosine Triphosphatases↗