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Biomedical subjects

R G Harrison

Publications and source records attributed to R G Harrison.

At least 19 recordsLinked to original sources
PubMed2002

Cosmic rays, clouds, and climate.

It has been proposed that Earth's climate could be affected by changes in cloudiness caused by variations in the intensity of galactic cosmic rays in the atmosphere. This proposal stems from an observed correlation between cosmic ray intensity and Earth's average cloud cover over the course of one solar cycle. Some scientists question the reliability of the observations, whereas others, who accept them as reliable, suggest that the correlation may be caused by other physical phenomena with decadal periods or by a response to volcanic activity or El Niño. Nevertheless, the observation has raised the intriguing possibility that a cosmic ray-cloud interaction may help explain how a relatively small change in solar output can produce much larger changes in Earth's climate. Physical mechanisms have been proposed to explain how cosmic rays could affect clouds, but they need to be investigated further if the observation is to become more than just another correlation among geophysical variables.

Journal Article↗
PubMed2001

A nonheme iron(II) complex that models the redox cycle of lipoxygenase.

The air-stable complex [Fe(6-Me3-TPA) (O2CAr)]+ [1; 6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine] has been synthesized as a model for the iron(II) site of lipoxygenase. This iron(II) complex reacts with 0.5 equiv ROOH to form a yellow species, which has been formulated as [FeIII(OH)(6-Me3-TPA) (O2CAr)]+ (2) by electrospray mass spectrometry. Addition of more ROOH converts 2 into a purple species, which is characterized by electrospray ionization mass spectrometry and resonance Raman spectroscopy as [FeIII(OOR)(6-Me3-TPA)(O2CAr)]+. The purple species is metastable and decomposes via Fe-O bond homolysis to regenerate the starting iron(II) complex. These metal-centered transformations parallel the changes observed for lipoxygenase in its reaction with its product hydroperoxide.

Cyclohexanes↗
PubMed2001

Do Wolbachia infections play a role in unidirectional incompatibilities in a field cricket hybrid zone?

Two closely related field crickets, Gryllus firmus and G. pennsylvanicus, hybridize along an extensive north-south zone in the eastern United States. Crosses between G. firmus males and G. pennsylvanicus females produce viable and fertile F1, but the reciprocal cross consistently fails to produce offspring. Wolbachia, a bacterial parasite of arthropods that causes unidirectional incompatibilities in a variety of insect species, has been suggested as the cause of the observed incompatibility between G. pennsylvanicus and G. firmus. We examine the presence/absence of Wolbachia strains, defined by sequencing the ftsZ gene, in four cricket populations from the north-eastern United States. Most G. firmus individuals are infected (100% in Guilford, Connecticut; 65% in Seaside Park, New Jersey) and > 95% of those infected harbour a single strain of Wolbachia. All individuals in G. pennsylvanicus populations (Ithaca, New York; Sharon, Connecticut) are infected; the majority of individuals carry a second strain of Wolbachia, but a significant fraction carry the same strain found commonly in G. firmus. The presence of an apparently identical Wolbachia strain in crickets of both species means that some crosses between G. pennsylvanicus males and G. firmus females should be compatible. We have no evidence of such compatibility. Furthermore, if Wolbachia infections are responsible for the observed incompatibility between species, then incompatibilities must also exist within G. pennsylvanicus, because this species harbours both Wolbachia strains. Although some single pair crosses within G. pennsylvanicus do fail to produce offspring, the proportion is lower than expected if Wolbachia were responsible. Therefore, Wolbachia is unlikely to be involved in reproductive isolation between the two cricket species.

Animals↗
PubMed2001

Variation in the dominant period during ventricular fibrillation.

Time-varying periodicities are commonly observed in biological time series. In this paper, we discuss three different algorithms to detect and quantify change in periodicity. Each technique uses a sliding window to estimate periodic components in short subseries of a longer recording. The three techniques we utilize are based on: 1) standard Fourier spectral estimation; 2) an information theoretic adaption of linear (autoregressive) modeling; and 3) geometric properties of the embedded time series. We compare the results obtained from each of these methods using artificial data and experimental data from swine ventricular fibrillation (VF). Spectral estimates have previously been applied to VF time series to show a time-dependent trend in the dominant frequency. We confirm this result by showing that the dominant period of VF, following onset, first decreases to a minimum and then rises to a plateau. Furthermore, our algorithms detect longer period correlations which may indicate the presence of additional periodic oscillations or more complex nonlinear structure. We show that in general this possibly nonlinear structure is most apparent immediately after the onset of VF.

Algorithms↗
PubMed2000

Metal-assembled cobalt(II) resorc[4]arene-based cage molecules that reversibly capture organic molecules from water and act as NMR shift reagents.

The complex Co4 1(2)8- is a tetranuclear cobalt(II) cage compound that assembles in aqueous solutions above pH 4 and is capable of encapsulating a variety of organic guest molecules, for example, benzene, hexane, chlorobutane, butanol, and ethyl acetate. Ligand 1 is a resorc[4]arene-based molecule with iminodiacetate moieties appended to its upper rim. 1H NMR studies of Co4 1(2)8-.guest complexes demonstrate inclusion of nonpolar hydrocarbons, substituted phenyls, alcohols, halogen-containing hydrocarbons, and polar organic molecules. The complex Co4 1(2)8- acts as an NMR shift reagent and causes substantial upfield isotropic hydrogen shifts (-30 to -40 ppm) in the guest molecule and separation of the guest hydrogen chemical shifts by typically 12 ppm. The complex Co4 1(2)8- will encapsulate molecules with fewer than eight atoms in a linear chain, mono- and disubstituted benzenes, and polar molecules with greater than two carbon atoms. The solid-state structure of Ba4[Co4 1(2).C6H5C2H5] shows a disordered guest molecule encapsulated within the cavity of Co4 1(2)8-. The cavity dimensions, bond lengths, and bond angles of Ba4[Co4 1(2).C6H5C2H5] are very similar to those determined in Ba4[Co4 1(2).6H2O].

Journal Article↗
PubMed2000

Mitochondrial DNA variation among worldwide populations of gypsy moths, Lymantria dispar.

Gypsy moth populations from Japan, mainland Asia, Europe, Tunisia, and North America were analyzed for variation in mitochondrial DNA (mtDNA) sequences from three gene regions. These samples resolve into four groups, representing gypsy moths from (1) Okinawa, Japan, (2) Hokkaido, Japan, (3) Honshu and Kyushu, Japan and mainland Asia, and (4) Europe, Tunisia, and North America. Some patterns of geographic variation observed for mtDNA (for example, the distinctiveness of gypsy moths from Hokkaido, Japan) coincide with those observed by Goldschmidt from analyses of morphology, life history, and intersexuality. Other patterns (relative sequence homogeneity across Asia, Honshu, and Kyushu and reduced levels of variation in mainland Japan) do not.

Animals↗
PubMed1999

New fusion protein systems designed to give soluble expression in Escherichia coli.

Three native E. coli proteins-NusA, GrpE, and bacterioferritin (BFR)-were studied in fusion proteins expressed in E. coli for their ability to confer solubility on a target insoluble protein at the C-terminus of the fusion protein. These three proteins were chosen based on their favorable cytoplasmic solubility characteristics as predicted by a statistical solubility model for recombinant proteins in E. coli. Modeling predicted the probability of soluble fusion protein expression for the target insoluble protein human interleukin-3 (hIL-3) in the following order: NusA (most soluble), GrpE, BFR, and thioredoxin (least soluble). Expression experiments at 37 degrees C showed that the NusA/hIL-3 fusion protein was expressed almost completely in the soluble fraction, while GrpE/hIL-3 and BFR/hIL-3 exhibited partial solubility at 37 degrees C. Thioredoxin/hIL-3 was expressed almost completely in the insoluble fraction. Fusion proteins consisting of NusA and either bovine growth hormone or human interferon-gamma were also expressed in E. coli at 37 degrees C and again showed that the fusion protein was almost completely soluble. Starting with the NusA/hIL-3 fusion protein with an N-terminal histidine tag, purified hIL-3 with full biological activity was obtained using immobilized metal affinity chromatography, factor Xa protease cleavage, and anion exchange chromatography.

Animals↗
PubMed1999

Pheromone binding proteins in the European and Asian corn borers: no protein change associated with pheromone differences.

Pheromone binding proteins (PBPs) are thought to play a role in the recognition of sex pheromone in male moth antennae. By binding selectively to different components of pheromone blends, these PBPs could play a role in differentiating between structurally related compounds. In this study we have characterized the pheromone binding proteins of two pheromone strains of the European corn borer (Ostrinia nubilalis) and also the closely related Asian corn borer (O. furnacalis). We have been able to detect only one PBP gene, which encodes a mature protein that is identical in amino acid sequence in individuals from different pheromone strains and different species. This result suggests that the PBP is not detecting differences between the two isomeric compounds of the European corn borer pheromone or the difference in double bond position between the pheromone molecules of the European and Asian corn borers.

Amino Acid Sequence↗
PubMed1999

Insights into genome differentiation: pheromone-binding protein variation and population history in the European corn borer (Ostrinia nubilalis).

Examination of sequence variation at nuclear loci can give insights into population history and gene flow that cannot be derived from other commonly used molecular markers, such as allozymes. Here, we report on sequence variation at a single nuclear locus, the pheromone-binding protein (PBP) locus, in the European corn borer (Ostrinia nubilalis). The European corn borer has been divided into three races in New York State on the basis of differences in pheromone communication and life history. Previous allozyme data have suggested that there is a small but significant amount of genetic differentiation between these races. The PBP does not appear to be involved in the pheromone differences between these races. Examination of variation at the PBP locus in the three races reveals no fixed differences between races despite high levels of polymorphism. There also appears to have been considerable recombination in the history of the pheromone-binding protein alleles. Observation of both recombination between alleles and lack of significant nucleotide or insertion/deletion divergence between races leads us to suggest that these populations are either recently diverged or have continued to exchange genetic material subsequent to divergence in pheromone communication and life history.

Animals↗
PubMed1999

Cytochrome b evolution in birds and mammals: an evaluation of the avian constraint hypothesis.

Patterns of molecular evolution in birds have long been considered anomalous. Compared with other vertebrates, birds have reduced levels of genetic divergence between groups of similar taxonomic ranks for a variety of nuclear and mitochondrial markers. This observation led to the avian constraint hypothesis, which identifies increased functional constraint on avian proteins as the cause for the reduction in genetic divergence. Subsequent investigations provided additional support for the avian constraint hypothesis when rates of molecular evolution were found to be slower in birds than in mammals in a variety of independent calibrations. It is possible to test the avian constraint hypothesis as an explanation for this avian slowdown by comparing DNA sequence data from protein-coding regions in birds and homologous regions in mammals. The increased selective constraints should lead to a reduction in the proportion of amino acid replacement substitutions. To test for such a decrease, we calculated the numbers of amino acid replacement substitutions per replacement site (dN) and silent substitutions per silent site (dS) for the complete mitochondrial cytochrome b gene using 38 avian and 43 mammalian comparisons that were phylogenetically independent. We find that dN/dS is significantly smaller in birds than in mammals. This difference cannot be explained by differences in codon bias affecting dS values. We suggest that the avian slowdown can be explained, at least in part, by a decreased tolerance for amino acid substitutions in avian species relative to mammalian species.

Animals↗
PubMed1998

Recombinant production and purification of novel antisense antimicrobial peptide in Escherichia coli.

A fusion protein was genetically engineered that contains an antimicrobial peptide, designated P2, at its carboxy terminus and bovine prochymosin at its amino terminus. Bovine prochymosin was chosen as the fusion partner because of its complete insolubility in Escherichia coli, a property utilized to protect the cells from the toxic effects of the antimicrobial peptide. This fusion protein was purified by centrifugation as an insoluble inclusion body. A methionine linker between prochymosin and the P2 peptide enabled P2 to be released by digestion with cyanogen bromide. Cation exchange HPLC followed by reversed-phase HPLC were used to purify the P2 peptide. The recombinant P2 peptide's molecular mass was confirmed by mass spectrometry to within 0.1% of the theoretical value (2480.9 Da), and the antimicrobial activity of the purified recombinant P2 against E. coli D31 was determined to be identical to that of the chemically synthesized peptide (minimal inhibitory concentration of 5 mg/mL). Although the yield of the fusion protein after expression by the cells was high (16% of the total cell protein), the percentage recovery of the P2 peptide in the inclusion bodies was relatively low, which appears to be due to losses in the cyanogen bromide digestion step.

Amino Acid Sequence↗
PubMed1997

Inferences about the origin of a field cricket hybrid zone from a mitochondrial DNA phylogeny.

Two closely related eastern North American field crickets, Gryllus firmus and G. pennsylvanicus, hybridize along a zone that extends from Connecticut and the Hudson River Valley, south along the eastern front of the Appalachian Mountains to at least Virginia. Here we use mitochondrial DNA (mtDNA) sequences to construct a population phylogeny for this pair of hybridizing cricket species. Using a phylogenetic approach, we attempt to discriminate between alternative population histories (secondary contact vs. primary intergradation) leading to formation of the hybrid zone. A strict consensus tree, based on > 1600 bp of the COI-COII region of the mtDNA genome, reveals four exclusive groups, which correspond to regional grouping of conspecific crickets. Surprisingly, the mtDNA sequence data do not reveal any synapomorphies for either G. pennsylvanicus or G. firmus. However, the mtDNA data do reveal a clear north-south split within each of the cricket species, a pattern not seen for morphological or other molecular characters. The biogeographical history of the north-south divergence events remains a puzzle. Observed gene genealogies support a model of secondary contact for the southern part of the hybrid zone. Sequence divergence data argue that lineages currently found in New York and New England were already distinct when this region became habitable following the most recent glaciation.

Animals↗
PubMed1997

Phylogeography and host association in a pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae).

Inferring the historical context of ecological diversification is an important step in understanding the way that population-level processes result in a diversity of species and interactions in communities. We performed a phylogeographic analysis of mitochondrial DNA haplotypes from the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) in order to determine the degree to which populations were structured according to geographical location and host-plant association. Ninety-eight individuals were sampled from 29 locations ranging from southern California to western Idaho. Restriction-site variation in 87 individuals (27 populations) was screened by digestion with 11 endonucleases, followed by Southern blotting; 38 restriction-site positions were mapped by double digests. Haplotypes were further defined by generating fragments 251 bases in length via PCR, screening them for sequence variation using denaturing gel gradient electrophoresis (DGGE), and sequencing the resulting variants. Parsimony analysis of the resulting 12 restriction-site and 15 sequence haplotypes indicated strong geographical structuring of populations: (i) most populations were monomorphic for haplotype; (ii) haplotypes from California and the Pacific Northwest (Oregon, Washington and Idaho) formed robust monophyletic groups. Population structure was significant both within and between the two regions, as reflected by NST. Patterns of host-plant association and haplotype phylogeny suggest that populations have recently undergone host-plant shifts in many different parts of the species range, although the direction and number of host shifts cannot be determined at the present level of sampling resolution.

Animals↗
PubMed1997

Balancing selection on electrophoretic variation of phosphoglucose isomerase in two species of field cricket: Gryllus veletis and G. offnsylvanicus.

Two species of crickets, Gryllus veletis and G. pennsylvanicus, share six electrophoretic mobility classes for the enzyme phosphoglucose isomerase (PGI), despite evidence from other genetic markers that the two species are not closely related within eastern North American field crickets. Moreover, the frequencies of the two most common PGI electrophoretic classes (PGI-100 and PGI-65) covary in sympatric populations of these species in the eastern United States, suggesting that PGI may be subject to trans-specific balancing selection. To determine the molecular basis of the electrophoretic variation, we characterized the DNA sequence of the Pgi gene from 29 crickets (15 G. veletis and 14 G. pennsylvanicus). Amino acid substitutions that distinguish the electrophoretic classes are not the same in the two species, and there is no evidence that specific replacement substitutions represent trans-specific polymorphism. In particular, the amino acids that diagnose the PGI-65 allele relative to the PGI-100 allele differ both between G. veletis and G. pennsylvanicus and within G. pennsylvanicus. The heterogeneity among electrophoretic classes that covary in sympatric populations coupled with analysis of patterns of nucleotide variation suggest that Pgi is not evolving neutrally. Instead, the data are consistent with balancing selection operating on an emergent property of the PGI protein.

Animals↗
PubMed1995

Comparison of the effects of hydrophobicity, amphiphilicity, and alpha-helicity on the activities of antimicrobial peptides.

Multiple linear regression was used to quantify the dependence of the antimicrobial activity of 13 peptides upon three calculated or experimentally determined parameters: mean hydrophobicity, mean hydrophobic moment, and alpha-helix content. Mean hydrophobic moment is a measure of the amphiphilicity of peptides in an alpha-helical conformation. Antimicrobial activity was quantified as the reciprocal of the measured minimal inhibitory concentration (MIC) against Escherichia coli. One of the peptides was magainin 2, and the remainder were novel peptides designed for this study. The multiple linear regression results revealed that the amphiphilicity of the peptides was the most important factor governing antimicrobial activity compared to mean hydrophobicity or alpha-helix content. A better regression of the data was obtained using ln(1/MIC+constant) as the dependent variable than with either 1/MIC or ln(1/MIC). These results should be useful in designing peptides with higher antimicrobial activity.

Amino Acid Sequence↗
PubMed1994

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data.

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.

Animals↗