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Biomedical subjects

R D Thompson

Publications and source records attributed to R D Thompson.

At least 73 records · Page 4Linked to original sources
PubMed1987

Identification of a transposon-like insertion in a Glu-1 allele of wheat.

The Glu-1 locus, present on the long arms of the group 1 chromosomes of wheat, codes for a group of storage protein polypeptides termed high molecular weight (HMW) subunits of glutenin. Hexaploid wheat varieties carry a 'silent' Glu-1y allele on chromosome 1A, no polypeptide being attributable to this locus. When two such alleles from different varieties were compared, one was found to contain an 8 kb insertion of DNA, termed Wis-2, interrupting the coding sequence. The insertion site is flanked by a 5 bp duplication. The two ends of Wis-2 contain similar sequences over 500 bp long and its termini contain almost the same short sequences but in opposite orientation. These terminal sequences are related to those of several 'retroposon'-type transposable elements found in other organisms.

Alleles↗
PubMed1986

Structure-activity relationships for N6-substituted adenosines at a brain A1-adenosine receptor with a comparison to an A2-adenosine receptor regulating coronary blood flow.

A series of 145 N6-substituted adenosines have been screened as inhibitors of the binding of [3H]cyclohexyladenosine to an A1-adenosine receptor in rat brain membranes and the results compared to the potencies of these analogs in increasing coronary blood flow via activation of an A2-adenosine receptor. The A1 receptor shows greater stereoselectivity in the N6 region of the receptor towards asymmetric aralkyl substituents, and shows greater bulk tolerance in the N6 region of the receptor such that it retains affinity for certain N6-tertiary alkyladenosines and N6-cycloalkyladenosines that are inactive at the coronary A2 receptor. At the A1 receptor, the most potent analogs have either aliphatic N6-substituents with four or more methylene residues or have an N6-halophenyl substituent. At the A2 receptor, the most potent analogs have an N6-phenethyl or similar heteroarylethyl substituent. Certain sets or series of analogs appear useful for identifying the subtypes of adenosine receptors involved in physiological functions.

Adenosine↗
PubMed1986

DNA restriction-fragment variation in the gene family encoding high molecular weight (HMW) glutenin subunits of wheat.

Restriction enzyme digests of DNA from nullisomic-tetrasomic and intervarietal chromosome substitution lines of wheat were probed with a high molecular weight (HMW) glutenin cDNA. Three restriction endonucleases were used to investigate restriction-fragment differences among five wheat varieties. The results suggest that the hybridizing fragments contain single gene copies and permit the identification of the subunit encoded by each gene. Restriction-fragment variation associated with previously established allelic differences between varieties was observed. Also, there is a clear relationship between the electrophoretic mobility of a HMW subunit and the length of the central repetitive section of the gene encoding it. These results are discussed with reference to the evolution of the HMW glutenin gene family and the uses of restriction-fragment variation in plant breeding and genetics.

Alleles↗
PubMed1986

Dog coronary artery adenosine receptor: structure of the N6-aryl subregion.

Previous structure-coronary vasoactivity correlations of the N6-alkyladenosine analogues of N6-[(R)-1-phenyl-2-propyl]adenosine, 1, support the hypothesis that the coronary artery A2 adenosine receptor contains an N6 region of specialized structure. The part of this receptor region that binds the 2-propyl moiety of 1 determines stereoselectivity and contributes to coronary vasoactivity. The present study uses 92 adenosine analogues containing an aryl group in the N6 substituent to test the hypothesis that the N6 receptor region contains an aryl subregion that binds the phenyl moiety of 1 and thereby contributes to its coronary vasoactivity. N6-Aralkyladenosines are often more potent than their alkyl congeners. Two methylene residues seem to provide optimum separation of the aryl group from N6. Among adenosines with semirigid N6 substituents, N6-[(1R,2S)-trans-2-phenylcyclohexyl]adenosine was uniquely active, evidence that when 1 occupies the receptor, the axis of the propyl C-1 to phenyl C-1 bond is nearly in the plane described by N6 and propyl C-1 and C-2. The torsion angle around this bond is unknown. Replacing the phenyl group of N6-2-phenethyladenosine with a thienyl or a 3-pyridyl group raises activity. The structure-activity relationships of the N6-(arylethyl)-, the N6-(arylmethyl)-, and the N6-phenyladenosines differ strinkingly from each other. Taken together, such results support the idea that the N6 region of the dog coronary artery A2 adenosine receptor includes an aryl subregion.

Adenosine↗
PubMed1986

N6-substituted N-alkyladenosine-5'-uronamides: bifunctional ligands having recognition groups for A1 and A2 adenosine receptors.

The coronary vasoactivity of N-ethyl-1'-deoxy-1'-(6-amino-9H-purin-9-yl)-beta-D-ribofuranuronamide (NECA, 1) is over 2 orders of magnitude greater than that of adenosine, and the vasoactivity of certain N6-substituted adenosines is as much as 1 order of magnitude greater. Such results suggest that a combination of appropriate modifications at N6 and C-5' might additively augment the agonist potency of adenosine. At low temperatures 1-deoxy-1-(6-chloro-9H-purin-9-yl)-2',3'-O-isopropylidene- beta-D-ribofuranosyl chloride (5), obtained in three steps from inosine, reacts with amines to yield uronamides. The subsequent reaction of such uronamides with amines at elevated temperatures displaces the purine 6-chloro group to yield, after deblocking, N-alkyl(or aryl)-N6-alk(ar)yl-adenosine-5'-uronamides. At the coronary artery A2 receptor the potency of N6-modified analogues of 1 is similar to that of the N6-substituted adenosine, rather than equal to or greater than 1. As agonists in the A2 receptor-mediated stimulation of adenylate cyclase in plasma membranes of PC12 pheochromocytoma cells or human platelets, N6-substituted analogues of 1 are intermediate between the high potency of 1 and the lower potency of the N6-substituted adenosines. At the A1 receptor of rat brain the potency of an N6-substituted analogue of 1 is often greater than that of the corresponding N6-substituted adenosine. At all four receptors, replacing the ethyl group of N-ethyl-N6-3-pentyladenosine-5'-uronamide by larger alkyl groups reduces potency; amides of secondary amines are inactive or have only marginal activity. Analogues of 1 containing a chiral center in the N6 substituent retain the stereoselectivity characteristic of each of the four receptors. Thus, at either A1 or A2 adenosine receptors, adenosine analogues interact with both the N6 and the C-5' receptor regions. However, the effects of N6 and C-5' modifications on potency are less than additive, evidence that the interaction of a substituent with its receptor region influences the interaction of other substituents with their respective receptor regions.

Adenosine↗
PubMed1985

Nucleotide sequence of a gene from chromosome 1D of wheat encoding a HMW-glutenin subunit.

A high molecular weight glutenin gene in hexaploid wheat has been isolated by cloning in bacteriophage lambda and characterized. The gene corresponds to polypeptide 12 encoded by chromosome 1D in the variety "Chinese Spring". The coding sequence predicted contains seven cysteine residues six of which flank a central repetitive region comprising more than 70% of the polypeptide. These findings are related to the role of high molecular weight subunits in the viscoelastic theory of gluten structure.

Amino Acid Sequence↗
PubMed1985

A method to classify airborne chemicals which alter the normal ventilatory response induced by CO2.

Guinea pigs inhaling 10% CO2, 19% O2, and 71 N2 increase their tidal volume (VT) by a factor of 2 to 3 and their respiratory frequency (f) by a factor of 1.2 to 1.5 above their normal values while breathing room air. While exposing guinea pigs to 10% CO2, a variety of aerosols can be added to determine how they modify the normal ventilatory response to this agent. Aerosols of carbamylcholine, serotonin, or propranolol all decreased VT of guinea pigs when added to 10% CO2. We propose here that chemicals evoking reductions in tidal volume can be classified into two groups based on the set of concurrent respiratory responses. Those chemicals evoking "obstruction," not only reduced VT but also decreased (f), increased resistance to airflow in conducting airways, and interrupted airflow. The prototype of this family would be carbamylcholine. The second group of chemicals evoked what is described as "reflex restriction." These agents reduced VT but increased f and lowered resistance to airflow. Propranolol would be the prototype for this family. Serotonin, however, evoked both types of response patterns which were time dependent. At the beginning of exposure, obstruction was prevalent while at the end of a 30-min exposure, reflex restriction was prevalent.

Aerosols↗
PubMed1985

Synthesis of a wheat storage protein subunit in Escherichia coli using novel expression vectors.

Useful plasmid expression vectors have been constructed which allow the synthesis of beta-galactosidase (betaG) fusion polypeptides or of polypeptides specified by cDNA clones in Escherichia coli hosts. A foreign DNA fragment can be inserted in any one of the three reading frames at the unique EcoRI, BamHI or SmaI sites immediately after the initiation codon. The cloned foreign gene is under the control of the lac promoter. Using a cDNA clone that encodes part of a wheat storage protein [a high-Mr (HMW) glutenin subunit] synthesis of a glutenin-beta G fusion protein was demonstrated. Synthesis of the glutenin polypeptide, not fused to beta G, was achieved by replacing the lacZYA genes with a stop codon.

Chromosome Mapping↗
PubMed1985

Dog coronary artery adenosine receptor: structure of the N6-alkyl subregion.

The moderately potent and stereoselective coronary vasoactivity of N6-[1-phenyl-2(R)-propyl]adenosine (1) is the basis for the present study that maps the N6 region of the coronary artery adenosine receptor by means of the structure-coronary vasoactivity relationships of 81 analogues of 1 in the open-thorax dog. Stereoselectivity is a general property of N6-substituted adenosines that have a chiral center adjacent to N6. The activity ratio of 1 to its S diastereomer is 10, the result of the positive interaction with the receptor of the propyl C-3 group of the R diastereomer in combination with the steric hindrance exerted by this group of the S diastereomer. Replacing the benzyl moiety of 1 by an ethyl, phenyl, phenethyl, or naphthyl group lowers potency of the R diastereomer and, accordingly, the R/S ratio. Propyl C-1 of 1 interacts with a receptor region large enough to accommodate three methylene residues and the propyl C-3 residue with a separate region large enough to accommodate two. The receptor subregion that interacts with the propyl C-1 of 1 is more tolerant of bulk and of polar substituents than the subregion that interacts with propyl C-3. Evidence bearing on the possible contribution of N6 to activity, e.g. through hydrogen bonding, is ambiguous. These results support a provisional model of the N6-alkyl subregion.

Adenosine↗
PubMed1984

Biological activity and a modified synthesis of 8-amino-3-beta-D-ribofuranosyl-1,2,4-triazolo[4,3-a]pyrazine, an isomer of formycin.

A two-step synthesis of 8-amino-3-beta-D-ribofuranosyl-1,2,4-triazolo[4,3-a]pyrazine (3), which is an isomer of formycin that resembles 3-deazaadenosine, is reported. Compound 3 is also described as as being a very poor substrate for adenosine deaminase and to be both a competitive and an irreversible inhibitor of S-adenosylhomocysteinase in the synthesis direction. L1210 cell growth in culture was inhibited by 3. Compound 3 was not converted to the nucleotide level in erythrocytes but was found to inhibit both the cellular uptake of nucleic acid precursors and their incorporation into the nucleic acids of L1210 cells. Finally, 3 was found to be a weak antiviral agent and coronary vasodilator.

Adenosine Deaminase↗
PubMed1983

The characterization of cDNA clones coding for wheat storage proteins.

Poly(A)+ RNA isolated from the developing wheat endosperm var. Chinese Spring, has been used as template for the construction of a cDNA library. Within the library, clones have been identified by in vitro translation of hybrid-selected mRNA which encode alpha/beta gliadin related sequences and gamma-gliadin related sequences. The DNA sequence of one such clone has been determined and it shows homology with that of a clone encoding a barley storage protein, B-hordein. The sequence includes a tandem DNA repeat which is discussed in relation to the generation of diversity within the gliadins.

Amino Acid Sequence↗
PubMed1983

Ligand selectivity of dog coronary adenosine receptor resembles that of adenylate cyclase stimulatory (Ra) receptors.

Adenosine receptors on the surface of coronary myocytes initiate coronary relaxation, but events subsequent to receptor occupancy are uncertain. We assayed the coronary vasoactivity of receptor-selective adenosine analogs in open chest dogs to test the hypothesis that the coronary adenosine receptor is an adenylate cyclase stimulatory (Ra) receptor. The potency order was: ethyl adenosine-5'-uronamide greater than cyclopropyl adenosine-5'-uronamide greater than 2-chloroadenosine greater than N6-[R(-)-1-phenyl-2-propyl] adenosine (R-PIA) greater than N6-cyclohexyladenosine greater than adenosine greater than S-PIA. Such a hierarchy of activity resembles that of the Ra receptors of thyroid and aortic myocyte adenylate cyclases and of tracheal smooth muscle relaxation. The potency order R-PIA greater than adenosine and the stereoselective coronary vasoactivity of R-PIA suggest that the coronary receptor may be a hybrid receptor which contains the "N6 site" typical of inhibitory (Ri) receptors in addition to the "5'-uronamide site' which expresses Ra activity.

Adenosine↗
PubMed1982

S1 and S2, the linear mitochondrial DNAs present in a male sterile line of maize, possess terminally attached proteins.

S1 and S2 are short linear mitochondrial DNA molecules found in a particular male sterile cytoplasm of maize. We show here that these DNA molecules and two other related linear DNA species found in maize mitochondria, have proteins attached, probably covalently, to their 5' ends. This is the first demonstration of such a linear DNA-terminal protein association in higher eukaryotes. Such proteins may be involved in priming replication of these DNAs.

DNA, Mitochondrial↗
PubMed1981

Molecular cloning and analysis of cDNA sequences derived from poly A+ RNA from barley endosperm: identification of B hordein related clones.

A collection of over 130 cDNA clones has been constructed in the bacterial plasmids pPH207 and pBR322 using as template the poly A+ RNA from membrane-bound polysomes of barley endosperm (cv. Sundance). Fifty four B hordein cDNA clones have been identified by cross-hybridization analysis and in vitro translation of plasmid-selected mRNAs. Hybridization of 11 of the B hordein cDNA clones to Northern blots of size-fractionated RNA indicated that the B hordein mRNA is ca. 1300 nucleotides long. One cDNA clone, pHvE-c16, has been partially sequenced and shown by comparison with C-terminal and other peptide sequences to be related to B1 hordein polypeptides. The results obtained from the analysis of the B hordein cDNA clones support the idea that the Hor 2 locus, which specifies the B hordeins, is complex and codes for a family of related mRNA species.

Base Sequence↗
PubMed1981

The integrated forms of the S1 and S2 DNA elements of maize male sterile mitochondrial DNA are flanked by a large repeated sequence.

The mitochondrial DNA of maize was cloned using the cosmid, Homer I. Recombinants carrying sequences homologous to the S1 and S2 DNA elements of male sterile maize have been analysed. Restriction endonuclease maps for Sac II, Sma I and Bam HI have been constructed. The S1 and S2 sequences are single copy sequences occurring at unique sites; each is flanked by a 26 kb repeated sequence. The repeated sequence has been shown not to contain the mitochondrial ribosomal RNA genes.

Base Sequence↗
PubMed1980

Variations in mitochondrial DNA organisation between normal and male-sterile cytoplasms of maize.

Mitochondrial DNA from male-sterile lines of maize carrying S cytoplasm contains two small DNA species which are absent from N (fertile) and other male-sterile cytoplasms. Portions of these species have been purified and amplified by constructing recombinant plasmids in vitro. Probes made with these plasmids have been used to demonstrate; i) a homologous region in the N mitochondrial genome, which may indicate the origin of the S specific DNA species. ii) two other DNA species present in low amounts in S cytoplasm only. iii) the absence of strong homology to the S specific DNA species in mitochondria from C and T male-sterile cytoplasms.

Cytoplasm↗
PubMed1980

Distribution of sequences common to the 25--28S-ribonucleic acid genes of Xenopus laevis and Neurospora crassa.

The extent of homology between the nucleotide sequence of L-rRNA (the major RNA component of the larger ribosomal subparticle) of a lower eukaryote (Neurospora crassa) and an amphibian (Xenopus laevis) was investigated by utilizing rDNA (DNA coding for rRNA) of X. laevis cloned in plasmids pMB9 and pML2, and rDNA of N. crassa cloned in bacteriophage lambda. Hybridization studies revealed that sequences common to both N. crassa and X. laevis L-rRNA comprise a total of approx. 1050 /+- 200 nucleotides. The thermal stability of the X. laevis rDNA.N. crassa L-rRNA hybrid was 5 degrees C lower than that of the X. laevis rDNA.X. laevis L-rRNA duplex, indicating the presence of fewer than 10% mismatches in homologous sequences. X. laevis rDNA was analysed by means of restriction endonucleases and hybridization with 125I-labelled N. crassa L-rRNA. Most (at least 95%) of the conserved sequences were present in a 3000-base-pair fragment produced by restriction with endonucleases HindIII and BamHI. This fragment, which includes the 3'-OH terminus of the L-rRNA-coding region, was used as an adaptor in the construction of a bacteriophage-lambda recombinant. One section of the recombinant phage terminating in a HindIII-specific site was obtained from bacteriophage lambda plac5 (after restriction with endonuclease HindIII). A second section terminating in a BamHi-specific site was obtained from bacteriophage lambda 540 (after restriction with endonuclease BamHI). These two parts were joined by means of the X. laevis rDNA fragment. Further analysis of cloned rDNA by means of restriction endonucleases confirmed that conserved sequences were widely distributed throughout the 3000-base-pair fragment produced by HindIII and BamHi endonucleases. A 3400-base-pair fragment of N. crassa rDNA cloned in a bacteriophage lambda [Cox & Peden (1979) Mol. Gen. Genet. 174, 17--24] was restricted with endonucleases. The products were hybridized with 125I-labelled X. laevis L-rRNA. Conserved sequences were shown to be distributed over a range of approx. 1600--2700 base-pairs. Hence, in neither X. laevis nor N. crassa L-rRNA can be conserved sequences from a single block; instead regions of high and low (or no) homology must be intermingled. Both N. crassa rDNA and X. laevis rDNA were found to hybridize with Drosophila melanogaster L-rDNA sequences. Those rDNA fragments with sequences common to X. laevis and N. crassa L-rRNA also hybridized with D. melanogaster L-rRNA probe. Thus the same set of conserved sequences may be present in all three species.

Animals↗