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T M Jenkins

Publications and source records attributed to T M Jenkins.

At least 37 records · Page 2Linked to original sources
PubMed1996

Cytoplasmic incompatibility and mating preference in Colombian Drosophila pseudoobscura.

MACRAE and ANDERSON observed a large frequency change of mitochondrial DNA (mtDNA) haplotypes in a population initiated with two allopatric strains of Drosophila pseudoobscura, BogER from Colombia and AH162 from California. They concluded that mtDNA haplotypes in D. pseudoobscura are not always selectively neutral. NIGRO and PROUT suggested, however, that a maternally transmitted incompatibility system, similar to the one they observed in two strains of D. simulans from Italy, could account for the observed mtDNA frequency changes. SINGH and HALE postulated that a mating preference between the strains BogER and AH162 in MACRAF and ANDERSON's experiment, in the form of negative assortative mating, could also account for the mtDNA frequency changes. We report two experiments designed to test the hypotheses: that a maternally transmitted cytoplasmic incompatibility system exists between D. pseudoobscura strains BogER and AH162; and, that BogER females mate preferentially with AH162 males. Our results do not support either hypothesis.

Animals↗
PubMed1996

Mitochondrial gene divergence of Colombian Drosophila pseudoobscura.

Isolated populations of drosophila pseudoobscura, separated from North American populations by about 2,400 km, were found in Colombia in 1960. We compared for sequences of the small ribosomal RNA (srRNA) gene on the mitochondria between North American and Colombian D. pseudoobscura in order to clarify the age of the Colombian isolates. The North American populations were not genetically different from each other but were genetically different from the Colombian populations. The Mexican strains represent the area from which the Colombian founders might have come. The estimated net nucleotide divergence between Mexican and Colombian D. pseudoobscura indicates that the Colombian population is not an ancient lineage. Phylogenies using both distance and parsimony methodologies reinforced this conclusion. The Colombian samples group together with both methods but, according to the bootstrap analysis, not significantly. It appears that the populations have not been separated long enough for their DNA sequences to show much divergence.

Animals↗
PubMed1996

Radiation protection systems for the final focus test beam at SLAC.

The Final Focus Test Beam (FFTB) is a new beam line at the Stanford Linear Accelerator Center designed to test new beam optics concepts, hardware, and techniques necessary to achieve and measure the small spot sizes required for future generations of high-energy e+e- linear colliders. The FFTB takes a 47 GeVc-1, 1 kW electron beam at the end of the Stanford Linear Accelerator Center linear accelerator and transports it to the FFTB beam dump. A radiation protection system was designed and installed for the FFTB with the primary goal that the integrated dose equivalent outside the shielding resulting from beam loss would not exceed 10 mSv y-1. This system is comprised of shielding, a beam containment system and a personnel protection system. This paper presents various aspects of radiation safety at Stanford Linear Accelerator Center that were considered in the design of the FFTB radiation protection system. Beam tests were conducted in which the performance of various beam containment devices and the shielding effectiveness were evaluated. Preliminary results from these tests are presented.

California↗
PubMed1995

Catalytic domain of human immunodeficiency virus type 1 integrase: identification of a soluble mutant by systematic replacement of hydrophobic residues.

The integrase protein of human immunodeficiency virus type 1 is necessary for the stable integration of the viral genome into host DNA. Integrase catalyzes the 3' processing of the linear viral DNA and the subsequent DNA strand transfer reaction that inserts the viral DNA ends into host DNA. Although full-length integrase is required for 3' processing and DNA strand transfer activities in vitro, the central core domain of integrase is sufficient to catalyze an apparent reversal of the DNA strand transfer reaction, termed disintegration. This catalytic core domain, as well as the full-length integrase, has been refractory to structural studies by x-ray crystallography or NMR because of its low solubility and propensity to aggregate. In an attempt to improve protein solubility, we used site-directed mutagenesis to replace hydrophobic residues within the core domain with either alanine or lysine. The single substitution of lysine for phenylalanine at position 185 resulted in a core domain that was highly soluble, monodisperse in solution, and retained catalytic activity. This amino acid change has enabled the catalytic domain of integrase to be crystallized and the structure has been solved to 2.5-A resolution [Dyda, F., Hickman, A. B., Jenkins, T. M., Engelman, A., Craigie, R. & Davies, D. R. (1994) Science 266, 1981-1986]. Systematic replacement of hydrophobic residues may be a useful strategy to improve the solubility of other proteins to facilitate structural and biochemical studies.

Amino Acid Sequence↗
PubMed1994

Crystal structure of the catalytic domain of HIV-1 integrase: similarity to other polynucleotidyl transferases.

HIV integrase is the enzyme responsible for inserting the viral DNA into the host chromosome; it is essential for HIV replication. The crystal structure of the catalytically active core domain (residues 50 to 212) of HIV-1 integrase was determined at 2.5 A resolution. The central feature of the structure is a five-stranded beta sheet flanked by helical regions. The overall topology reveals that this domain of integrase belongs to a superfamily of polynucleotidyl transferases that includes ribonuclease H and the Holliday junction resolvase RuvC. The active site region is identified by the position of two of the conserved carboxylate residues essential for catalysis, which are located at similar positions in ribonuclease H. In the crystal, two molecules form a dimer with a extensive solvent-inaccessible interface of 1300 A2 per monomer.

Amino Acid Sequence↗
PubMed1992

DNA polymerase beta and DNA synthesis in Xenopus oocytes and in a nuclear extract.

The identities of the DNA polymerases required for conversion of single-strand (ss) M13 DNA to double-strand (ds) M13 DNA were examined both in injected Xenopus laevis oocytes and in an oocyte nuclear extract. Inhibitors and antibodies specific to DNA polymerases alpha and beta were used. In nuclear extracts, inhibition by the antibody to polymerase beta could be reversed by purified polymerase beta. The polymerase beta inhibitors, dideoxythymidine triphosphate (ddTTP) and dideoxycytidine triphosphate (ddCTP), also blocked DNA synthesis and indicated that polymerase beta is involved in the conversion of ssDNA to dsDNA. These results also may have particular significance for emerging evidence of an ssDNA replication mode in eukaryotic cells.

Animals↗
PubMed1991

Hydrogenosomal succinate thiokinase in Tritrichomonas foetus and Trichomonas vaginalis.

Succinate thiokinase displays a diversity of nucleotide specificity and molecular size throughout Nature. Eukaryotes and Gram-positive bacteria possess distinct 'small' (dimeric) thiokinase enzymes which are specific for adenine (ADP) or guanine (GDP) nucleotides, whereas Gram-negative bacteria contain a single 'large' (tetrameric) enzyme which utilizes both nucleotides. Succinate thiokinase activities, both ADP- and GDP-dependent, were shown to be hydrogenosomal in Tritrichomonas foetus and Trichomonas vaginalis. Surprisingly, the 'small' enzyme was found in T. foetus whereas T. vaginalis contained a 'large' enzyme.

Adenosine Diphosphate↗
PubMed1988

Physiological roles of animal succinate thiokinases. Specific association of the guanine nucleotide-linked enzyme with haem biosynthesis.

The discovery of two distinct succinate thiokinases in mammalian tissues, one (G-STK) specific for GDP/GTP and the other (A-STK) for ADP/ATP, poses the question of their differential metabolic roles. Evidence has suggested that the A-STK functions in the citric acid cycle in the direction of succinyl-CoA breakdown (and ATP formation) whereas one role of the G-STK appears to be the re-cycling of succinate to succinyl-CoA (at the expense of GTP) for the purpose of ketone body activation. A third metabolic participation of succinyl-CoA is in haem biosynthesis. This communication shows that in chemically induced hepatic porphyria, when the demand for succinyl-CoA is increased, it is the level of G-STK only which is elevated, that of A-STK being unaffected. The results implicate G-STK in the provision of succinyl-CoA for haem biosynthesis, a conclusion which is further supported by the observation of a high G-STK/A-STK ratio in bone marrow.

Acyl Coenzyme A↗
PubMed1988

Two distinct succinate thiokinases in both bloodstream and procyclic forms of Trypanosoma brucei.

Two succinate thiokinase activities specific for either adenine or guanine nucleotides have been found in Trypanosoma brucei. Key glycolytic and citric acid cycle enzymes were measured to show repression of glycolysis and derepression of the citric acid cycle in the procyclic form, relative to the bloodstream form. A marked rise in adenine-linked succinate thiokinase activity accompanied a rise in activity of citric acid cycle enzymes. However, guanine-linked succinate thiokinase was found to increase only slightly in activity. These results implicate the adenine-linked enzyme as an essential component of the citric acid cycle, whereas the guanine-linked enzyme appears to be under separate control. This communication also reports for the first time the occurrence of citrate synthase activity in the bloodstream (long slender) form of T. brucei.

Adenine Nucleotides↗
PubMed1986

Distinct physiological roles of animal succinate thiokinases. Association of guanine nucleotide-linked succinate thiokinase with ketone body utilization.

Two distinct succinate thiokinases have recently been shown to exist in animal tissues, one specific for guanine nucleotide and the other for adenine nucleotide. Their physiological roles have here been investigated by comparing the levels of the two enzymes in liver and brain of normal and diabetic rats. A marked rise in the level of brain guanine nucleotide-linked succinate thiokinase in the diabetic condition is consistent with an enhanced utilization of ketone bodies and hence with the associated elevated demand for succinyl-CoA for the activation of acetoacetate. Taken together with the reported mitochondrial values of the ATP/ADP and GTP/GDP ratios, the results are interpreted to indicate that the adenine nucleotide-linked enzyme functions as a component of the citric acid cycle whereas the guanine nucleotide-linked enzyme functions in the opposite metabolic direction to produce succinyl-CoA from succinate.

Adenosine Triphosphate↗