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K S Jones

Publications and source records attributed to K S Jones.

9 recordsLinked to original sources
PubMed1992

Retroviral integrase functions as a multimer and can turn over catalytically.

A number of studies have demonstrated that the retroviral protein integrase (IN) alone is sufficient to carry out two discrete steps required for retroviral integration: the endonucleolytic processing of viral DNA ends and the cleavage and joining of host DNA to the processed viral DNA termini. Little is known about the biochemical and biophysical mechanisms involved in these reactions. Here, we employ in vitro assays of Rous sarcoma virus IN to demonstrate for the first time that IN is capable of multiple turnover in both the processing and joining reactions. The turnover number calculated for the processing reaction is 0.26 cleavages/min/mol of IN. Our steady state kinetic studies indicate that both the processing and joining activities require a multimeric form of IN. Ultracentrifugation analyses reveal a substrate-independent reversible equilibrium among the monomeric, dimeric, and tetrameric forms of this protein. From these results we conclude that the minimal functional unit for both the processing and joining of each viral DNA end is an IN dimer.

Animals↗
PubMed1992

Residues critical for retroviral integrative recombination in a region that is highly conserved among retroviral/retrotransposon integrases and bacterial insertion sequence transposases.

Our comparison of deduced amino acid sequences for retroviral/retrotransposon integrase (IN) proteins of several organisms, including Drosophila melanogaster and Schizosaccharomyces pombe, reveals strong conservation of a constellation of amino acids characterized by two invariant aspartate (D) residues and a glutamate (E) residue, which we refer to as the D,D(35)E region. The same constellation is found in the transposases of a number of bacterial insertion sequences. The conservation of this region suggests that the component residues are involved in DNA recognition, cutting, and joining, since these properties are shared among these proteins of divergent origin. We introduced amino acid substitutions in invariant residues and selected conserved and nonconserved residues throughout the D,D(35)E region of Rous sarcoma virus IN and in human immunodeficiency virus IN and assessed their effect upon the activities of the purified, mutant proteins in vitro. Changes of the invariant and conserved residues typically produce similar impairment of both viral long terminal repeat (LTR) oligonucleotide cleavage referred to as the processing reaction and the subsequent joining of the processed LTR-based oligonucleotides to DNA targets. The severity of the defects depended upon the site and the nature of the amino acid substitution(s). All substitutions of the invariant acidic D and E residues in both Rous sarcoma virus and human immunodeficiency virus IN dramatically reduced LTR oligonucleotide processing and joining to a few percent or less of wild type, suggesting that they are essential components of the active site for both reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

A technique for the preparation of cross-sectional TEM samples of ZnSe/GaAs heterostructures which eliminates process-induced defects.

Cross-sectional transmission electron microscopy (TEM) sample preparation of ZnSe/GaAs epitaxial films is investigated. Conventional argon ion milling is shown to produce a high density (approximately 5-8 x 10(11)/cm2) of small (diameter approximately 60-80 A) extended defects (stacking faults, microtwins, double positioning twins, etc.). In addition, transmission electron diffraction results indicate a thin ZnO layer can also occasionally form upon ion milling or electron-beam irradiation although the exact conditions for ZnO formation are not well understood. Conventional TEM (amplitude contrast) and high-resolution TEM (phase contrast) imaging in combination with transmission electron diffraction studies were performed to determine the optimum method of removing the ion milling related damage and ZnO layers during sample preparation. HF/HCl, NaOH/H2O, H2SO4/H2O2/H2O and Br2/CH3OH etching mixtures as well as low voltage argon or iodine ion milling were studied. A low energy (2 keV) iodine or argon ion milling step was shown to remove the ZnO layer and reduced the density of the extended defects associated with Ar+ ion milling, but was unsuccessful in removing all of the defects. Auger electron spectroscopy results indicate residual iodine was either left on the surface or implanted beneath the surface during iodine ion milling. Etching the XTEM samples in HF/HCl was shown to be effective in removing the ZnO layer but had little or no effect on the ion milling induced defects. Etching the samples in a 0.5% Br2/CH3OH solution resulted in complete elimination of the ion milling induced extended defects including the residual defects associated with iodine ion milling. In addition the Br2/CH3OH etch produced the best surface morphology. Thus a brief (1-2 seconds) Br2/CH3OH etch after conventional preparation (argon ion milling) of cross-sectional ZnSe/GaAs TEM samples appears to be an inexpensive and superior alternative to iodine ion milling.

Arsenic↗
PubMed1991

Identification and characterization of intragenic sequences which repress human immunodeficiency virus structural gene expression.

Examination of the life cycle of the human immunodeficiency virus (HIV) has shown that multiple levels of regulation exist, including some which require the virus-encoded Rev protein. In the absence of Rev, mRNAs encoding the structural proteins remain untranslated, a phenomenon which appears, in part, to be caused by nuclear entrapment of these RNA species. To examine the basis for repression of structural gene mRNA expression, a heterologous assay system was utilized to determine whether regions present within gag and pol contain elements capable of suppressing gene expression when present in cis. Both genes were found to contain cis-acting repressor sequences (CRS) that block gene expression when present within the 3' untranslated portion of a heterologous gene transcript. The element within pol was found to have the strongest repressive effect. While Rev alone was unable to reverse the repression observed with the pol sequence, addition of the env Rev-responsive element (RRE) in cis and Rev in trans did cause reversal of inhibition. Deletion mutagenesis defined a 260-bp element within the 3' portion of pol that contains a potent CRS which functions when present in the sense orientation. The corresponding region in HIV-2 pol was found to contain a functionally similar CRS element. To examine the mechanism of repression, the effects of the CRS elements on both the abundance and subcellular distribution of the mRNAs were examined. Neither was dramatically altered when examined in the context of a heterologous reporter (chloramphenicol acetyltransferase) mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Triage.

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Australia↗
PubMed1976

Health redefined.

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Australia↗
PubMedDate not supplied

Effects of listener sophistication on respiration audiometry.

Thirty normal-hearing college-age adults were tested by standard and respiration audiometry (RA) at 1000 Hz to investigate the effects of subject knowledge of the RA procedure. Three levels of sophistication were employed: (1) no knowledge, (2) full knowledge, and (3) deception. No significant effects on RA thresholds were revealed as a function of subject knowledge. RA itself was found to be less satisfactory as a means of measuring auditory threshold because of the difficulty in obtaining responses from some subjects and the degree of subjectivity required to judge responses.

Audiometry↗