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J D Love

Publications and source records attributed to J D Love.

6 recordsLinked to original sources
PubMed1992

Ultraviolet-induced dimerization of non-adjacent pyrimidines in poly[d(A-T)].

The DNA photoproduct responsible for the ultraviolet (UV) light-induced -1 frameshift mutation remains unknown. We recently identified a UV photoproduct consisting of a cyclobutane dimer occurring between non-adjacent thymine residues in the same strand, [sequence: see text] and proposed that replication across this unrepaired photoproduct might result in a -1 frameshift mutation since the intervening base is extrahelical. Until now this novel photoproduct has only been identified in single-stranded DNA polymers and does not occur in UV-irradiated double-stranded polymers due to conformational restraint. This observation suggested that this photoproduct could only occur in vivo in chromosomal sites that were single-stranded. In the current work the cis-syn dithymine cyclobutane dimer has been identified in the self-complementary polymer poly[d(A-T)] when UV irradiated in solution conditions (concentrated manganese chloride or 60% ethanol plus trace salts) wherein this polymer remains double-stranded but the double-helix is partially destabilized. Taken together, the current findings suggest that dipyrimidine photoproducts between non-adjacent residues on the same strand could occur in vivo in double-stranded, but partially destabilized, DNA.

Base Sequence↗
PubMed1986

Hydrogen peroxide toxicity may be enhanced by heat shock gene induction in Drosophila.

Recent evidence suggests that low dose exposure of cells to hydrogen peroxide and/or induction of heat shock protein (HSP) synthesis will render cells resistant to the lethal effects of a subsequent high dose hydrogen peroxide stress. We explored this possibility in the Drosophila melanogaster Schneider tissue culture line 2. It was found that chronic low dose exposure (1 mM H2O2 for 3 days) resulted in marked potentiation of the toxic effects of a subsequent high dose exposure (50 mM H2O2 for 1 h), as assessed by impairment of uridine incorporation and cell proliferation. Cells preexposed to low dose H2O2 exhibited enhanced heat shock gene transcription upon exposure to high dose H2O2, as compared to cells that did not receive low dose preexposure. Transcriptional induction of the heat shock genes by a mild non-toxic heat shock resulted in marked enhancement of the anti-proliferative effects of a subsequent H2O2 exposure. Thus, low dose hydrogen peroxide exposure or mild heating results in subsequent enhancement of high dose hydrogen peroxide toxicity; this effect correlates with enhanced heat shock gene expression. Possible mechanisms are discussed.

Animals↗
PubMed1985

Screening of lambda library for differentially expressed genes using in vitro transcripts.

We present an improved approach to the screening of eucaryotic libraries for differential gene expression. Previous techniques have generated probe via the harvesting of cellular poly(A)+ RNA and synthesizing labeled cDNA probe using reverse transcriptase. In our approach we prepare labeled RNA probe via in vitro transcription. Unlike cDNA preparation, in vitro transcription (i) directly reflects the ongoing rate of gene expression, and (ii) allows one to assess expression of genes whose transcripts are not polyadenylated. To make this approach practical for the screening of a large library, we modified and optimized existing in vitro transcription techniques, enhancing manyfold the [alpha-32P]UTP incorporation into mRNA, while almost completely suppressing rRNA incorporation. In addition, we developed a simple procedure for making precise replicate dot blots of very large quantities of lambda-phage library DNA. By combining our techniques of in vitro transcription and replicate blotting, we are able to approach detection of a twofold difference in gene expression over a greater than 1000-fold range in overall expression. Our single-clone amplification and dot-blotting technique resulted in nearly the same number of lambda-phage DNA copies per dot for all members of the library. This feature allows us to assign genes to different expression classes, as well as to detect any alterations in expression. We demonstrate our approach by screening the drosophila genomic DNA library with in vitro transcripts from drosophila tissue culture cells. Screening of the entire drosophila genomic library at the 99% probability level is readily achieved.

Animals↗
PubMed1979

The relationship between human serum and human pancreatic DNase I.

Deoxyribonuclease (DNase) activities have been partially purified from human serum and pancreas. Several of their physical and enzymatic characteristics were determined and compared in order to evaluate their relatedness. Human serum deoxyribonuclease has an isoelectric point in the range of 3.9 to 4.3 and a molecular weight of 33,000 to 38,000. Optimal enzymatic activity at pH 7.0 was dependent on both Mg2+ and Ca2+, whereas a pH optimum of from 5.5 to 5.8 was observed in the presence of Mg2+ and ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA). The proportion of single strand or double strand breakage products at early stages of DNA digestion were variable functions of the composition of the buffers employed for the reactions. Single strand break age was predominant under all reaction conditions. Double strand breakage occurred with greatest frequency under neutral conditions in the presence of Mg2+ and Ca2+, was inhibited by the inclusion of 0.15 M NaCl, and did not occur at pH 5.8 in the presence of Mg2+, EGTA, and 0.15 M NaCl. Human pancreas deoxyribonuclease exhibited essentially the same physical properties and enzymatic characteristics as those of the human serum enzyme. Thus, human serum deoxyribonuclease may originate in this pancreas.

Calcium↗