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R G Harrison

Publications and source records attributed to R G Harrison.

At least 19 recordsLinked to original sources
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↗
PubMed1991

Predicting the solubility of recombinant proteins in Escherichia coli.

We have studied the cause of inclusion body formation in Escherichia coli grown at 37 degrees C using statistical analysis of the composition of 81 proteins that do and do not form inclusion bodies. Six composition derived parameters were used. In declining order of their correlation with inclusion body formation, the parameters are charge average, turn forming residue fraction, cysteine fraction, proline fraction, hydrophilicity, and total number of residues. The correlation with inclusion body formation is strong for the first two parameters but weak for the last four. This correlation can be used to predict the probability that a protein will form inclusion bodies using only the protein's amino acid composition as the basis for the prediction.

Amino Acids↗
PubMed1991

Phylogenetic relationships of neopterygian fishes, inferred from mitochondrial DNA sequences.

To investigate the relationships among the three main groups of extant neopterygian fishes--Amiidae, Lepisosteidae, and Teleostei--we sequenced fragments of three mitochondrial genes from 12 different actinopterygian fishes and translated the nucleotide sequences into amino acid sequences. When all three regions are considered together, Amiidae clusters with Lepisosteidae in the most parsimonious cladograms, but other clades, such as Neopterygii and Teleostei, that are well supported by morphological evidence fail to emerge as monophyletic. When the cytochrome b sequences are analyzed together with previously published sequences for other taxa, the majority-rule consensus tree is consistent with the monophyly of Teleostei and Neopterygii and marginally supports the Amiidae + Lepisosteidae clade. In either analysis, when Neopterygii and Teleostei are constrained to monophyly, all the most-parsimonious cladograms support the Amiidae + Lepisosteidae topology. Where molecules and morphology disagree, provisional morphology-based constraints on the analysis of molecular data offer a practical means of integrating the two types of data.

Amino Acid Sequence↗
PubMed1990

Ultrastructure of proteoglycans in the tectorial membrane.

The ultrastructure of proteoglycans (PGs) in the tectorial membrane (TM) of the mature chinchilla cochlea was investigated using the cationic dye Cuprolinic blue. When used at a high critical electrolyte concentration, Cuprolinic blue has been shown specifically to bind to the glycosaminoglycan residues of sulfated PGs. After Cuprolinic blue treatment, PGs were observed in the TM which were represented as rod-shaped, electron-dense structures. A perifibrillar, primarily orthogonal, array of PGs was associated with the type A protofibrils. These PGs were distributed in 50 nm intervals along the length of the type A protofibrils. A less common orientation was parallel to the axis of the type A protofibrils. PGs did not appear to be associated with the type B protofibrils. Based upon previous results by other investigators, the TM contains types II and IX collagen, and it appears likely that the type A protofibrils are composed of collagen type II. PGs visualized in the TM in this study thus may represent the glycosaminoglycan residue of type IX collagen which is associated with the type II collagen fibrils. Alternatively, the TM PGs may be small dermatan or chondroitin sulfate PGs.

Animals↗
PubMed1989

Molecular population genetics of mtDNA size variation in crickets.

Nucleotide sequence analysis of a region of cricket (Gryllus firmus) mtDNA showing discrete length variation revealed tandemly repeated sequences 220 base pairs (bp) in length. The repeats consist of 206 bp sequences bounded by the dyad symmetric sequence 5'GGGGGCATGCCCCC3'. The sequence data showed that mtDNA size variation in this species is due to variation in the number of copies of tandem repeats. Southern blot analysis was used to document the frequency of crickets heteroplasmic for two or more different-sized mtDNAs. In New England populations of G. firmus and a close relative Gryllus pennsylvanicus approximately 60% of the former and 45% of the latter were heteroplasmic. From densitometry of autoradiographs the frequencies of mtDNA size classes were determined for the population samples and are shown to very different in the two species. However, in populations where hybridization between the two species has occurred, the frequencies of size classes and cytoplasmic genotypes in each species' distinct mtDNA lineage were shifted in a manner suggesting nuclear-cytoplasmic interactions. The data were applied to reported diversity indices and hierarchical statistics. The hierarchical statistics indicated that the greatest proportion of variation for mtDNA size was due to variation among individuals in their cytoplasmic genotypes (heteroplasmic or homoplasmic state). The diversity indices were used to estimate a per-generation mutation rate for size variants of 10(-4). The data are discussed in light of the relationship between genetic drift and mutation in maintaining variation for mtDNA size.

Animals↗
PubMed1988

High level expression of heterologous proteins in methylotrophic yeast Pichia pastoris.

Expression of human tumor necrosis factor-alpha (TNF) and four different TNF analogs has been studied in Pichia pastoris by utilizing the alcohol oxidase gene promoter. TNF expression level in certain transformants accounted for as much as 36% of the soluble protein. TNF expression was stably maintained during high cell density fermentation (100 g dry cell weight/liter) resulting in a TNF production level of 6-10 g/liter. TNF contained in P. pastoris cell lysates was biologically active as determined by its cytotoxic effect on murine L-929 fibroblast cells and the bioactivity was retained for at least 6 months in the lysates stored frozen at -20 degrees C in the presence of protease inhibitor PMSF. TNF expressed in P. pastoris was recognized by monoclonal antibodies prepared against recombinant Escherichia coli derived TNF. TNF purified from P. pastoris has the expected N-terminal amino acid sequence and specific activity of 10(7) units/mg protein. TNF analogs were also expressed at levels comparable to that of native TNF. Three of the four analogs were insoluble when produced in P. pastoris.

Densitometry↗
PubMed1986

Food deprivation reveals strain differences in opiate intake of Sprague-Dawley and Wistar rats.

Two groups of naive, male, albino rats derived from different genetic strains (Sprague-Dawley and Wistar) were given a 5 micrograms/ml etonitazene solution as their only available liquid. Liquid intake and body weights were recorded every 24 hr. Etonitazene intake was compared to baseline water intake, and drug intake was then compared when the rats were food deprived (25 sessions) and food satiated (24 sessions). Both groups drank similar amounts of water and etonitazene during the initial food satiation phase, although drug intake was slightly below water intake. When they were food deprived, the Wistar group's mean etonitazene intake almost doubled, while the Sprague-Dawley group's drug intake decreased by nearly 50%. The etonitazene intake in the Sprague-Dawley group never exceeded that of the vehicle, water; thus, it appeared that the drug was not functioning as a reinforcer. Food deprivation increased etonitazene intake above water levels in the Wistar group, indicating that the drug was serving as a reinforcer. Both groups showed similar drug effects during food deprivation, such as erratic drinking patterns, self-mutilation and other forms of stereotypy. Thus, both strains were sensitive to etonitazene's effects; they appeared to differ only with respect to the reinforcing effects. These results suggest that genetically-based differences in the reinforcing effects of drugs may be revealed by food deprivation.

Animals↗
PubMed1986

A computer-assisted morphometric analysis of the organ of Corti.

This paper describes a method for a computer-assisted morphometric analysis of the organ of Corti and presents normal morphometric data on the chinchilla cochlea. The computer-assisted light microscope system that we developed consists of commercially available equipment: an Olympus light microscope, Boeckler X, Y motorized stage micrometers, an IBM PC computer and a computer program written by the second author. The system was developed for the analysis of whole-mount, surface preparations of the organ of Corti. The procedure for producing suitable surface preparations for a computer-assisted analysis of hair cells was described in a previous paper (Santi, 1986). The analysis procedure requires 2 passes along the length of the basilar membrane. During the first pass, the system establishes an X, Y slide coordinate system and maps basilar membrane distance onto the coordinate system. This procedure was performed in approximately 10 min using an efficient, 3-point arc approximation method. During the second pass, the user scans along the length of the basilar membrane and measures organ of Corti structures (e.g., hair cell dimensions) or records abnormal or missing hair cells. In addition to providing distance along the length of the basilar membrane, the system could also determine which hair cell row the user was examining. Thus, recording damaged and missing hair cells consisted of merely pressing the appropriate footpedal to indicate the type and degree of hair cell damage. After assessing hair cell damage, a cytocochleogram with an accompanying table of descriptive statistics was produced. Since the X,Y coordinate system for each slide was stored on a disk along with its corresponding basilar membrane distance map, slides could be removed and later reevaluated without the loss of previously obtained data. Normal morphometric data on the chinchilla organ of Corti consisted of cell dimensions within the reticular lamina and a two-dimensional graphical reconstruction of the curvature of the basilar membrane.

Animals↗
PubMed1986

Mitochondrial DNA transmission genetics in crickets.

This paper presents the results of a single generation study of the transmission genetics of mitochondrial DNA in the field cricket Gryllus firmus. In this species, individuals heteroplasmic for at least two different-sized mitochondrial genomes can be collected easily from natural populations. The frequencies of mtDNA size variants in heteroplasmic females and samples of their offspring were estimated by densitometry of autoradiographs. The variance in mitochondrial genotype frequencies among the offspring of heteroplasmic females indicates that, through genetic drift, fixation would take several hundred animal generations. Differences between the observations and data on mtDNA transmission in yeast and cows are discussed in light of the differences in organelle sampling regime and early developmental events in these species. Our data also show shifts in genotype frequencies in the transmission from mother to offspring that suggest a bias in favor of smaller genomes. The nature of mtDNA size variation in natural populations of crickets is discussed in reference to a mutation-selection balance.

Animals↗
PubMed1982

A reexamination of rat ductuli efferentes.

In 33 testes from a random selection of rats a 10% suspension of India ink in normal saline was introduced through the rete testis into the emergent ductuli efferentes. Low-power microscopy and microradiography confirmed the individually independent origin of each ductule. Five ductules were isolated in each of 17 testes, 4 ductules in 6, 6 ductules in 8, and in 2 testes, 7 and 9 ductules, respectively. In six animals minor variations existed as between the right and left testes +/- 1 in 4 and +/- 2 in 2. It is necessary to exercise great caution in the interpretation of results of experimental work on alteration of the ductuli, because of variability between colonies and within strains of rats.

Animals↗
PubMed1982

Impairment of rat spermatogenesis following unilateral experimental ischemia.

When one testis in a rat is rendered ischemic, histologic damage occurs in the contralateral testis, which can be explained on immunologic grounds. An increase in the quantity of a naturally circulating cytotoxic antitestis antibody or an alteration in the specificity of this antibody was observed via cytotoxic antibody tests. Immunocytochemical techniques further demonstrated this phenomenon, showing binding of fluorescein-labeled antibody to sections of normal control testis or to sections of contralateral testis. It appeared that the ischemic testis presented altered ischemic cells or normal cells to the immune system as its blood-testis barrier was broken down. It is suggested that to leave a necrotic testis within the scrotum following prolonged torsion of the testis in the human may be a reason for subfertility or infertility in this type of condition, and a similar result may occur following unilateral testicular damage caused by varicocele or orchitis.

Animals↗