Biomedical subjects

R W Hammond

Publications and source records attributed to R W Hammond.

At least 37 records · Page 2Linked to original sources

PubMed1997

Capillary electrophoresis of supercoiled and linear DNA in dilute hydroxyethyl cellulose solution.

Capillary electrophoresis in dilute hydroxyethyl cellulose is shown to separate supercoiled DNA in the size range 2000-16,000 base pairs. The plasmids migrate more slowly than linear ds-DNA of the same sizes. Plasmid bandwidths are larger than observed for ds-DNA, allowing identification of the type of DNA by bandwidth. The differing dependence of mobility on chain length can be explained by assuming that a plasmid migrates as an elastic rod, while ds-DNA migrates as a wormlike chain.

Cellulose↗

PubMed1997

Variability of geographically distinct isolates of maize rayado fino virus in Latin America.

We have examined the molecular epidemiology of the leafhopper-borne maize rayado fino virus (MRFV) in Latin America. The coat protein gene and 3' non-translated region of 14 isolates of MRFV collected from Latin America and the United States were sequenced and phylogenetic relationships examined. The nucleotide sequence revealed remarkable conservation, with a sequence similarity of 88-99%. Phylogenetic analysis of sequence data obtained from a 633 bp fragment showed that MRFV has diverged into three main clusters, i.e. the geographically distinct northern and southern isolates and the Colombian isolates. Significant differences between the isolates collected from Colombia, previously named maize rayado colombiana virus, based upon differences in symptomatology and serological relationships to MRFV, and the other MRFV isolates, provides additional evidence supporting its designation as a unique strain of MRFV.

Amino Acid Sequence↗

PubMed1997

Destabilization of potato spindle tuber viroid by mutations in the left terminal loop.

Infectivity studies with highly infectious RNA inocula generated by ribozyme cleavage were used to compare the biological properties of three apparently nonviable mutants of potato spindle tuber viroid (PSTVd). One of these mutants (PSTVd-P) contains three nucleotide substitutions in the left terminal loop, and mechanical inoculation of tomato seedlings with RNA transcripts at levels equivalent to 10(3)-10(5) times the ID50 for PSTVd-Intermediate failed to result in systemic infection. Viable progeny containing a spontaneous C-->G change at position 4 could, however, be recovered from transgenic Nicotiana benthamiana plants that constitutively expressed PSTVd-P RNA. The initial mutations in PSTVd-P led to an overall weakening of its native structure in vitro, and the precisely-full-length molecule released by ribozyme cleavage in vivo was also unstable. Even RT-PCR analysis failed to reveal detectable amounts of circularized PSTVd-P among the RNAs isolated from uninfected plants. Predicted stabilizing effects of a spontaneous mutation at position 4 suggest that the appearance of viable progeny was dependent on a combination of events: errors by host RNA polymerase II during transcription of the mutant transgene coupled with a strong selective pressure against alterations in the native structure of PSTVd.

Mutation↗

PubMed1997

Treatment of ocular bacterial infections: an update.

BACKGROUND: Because of increased bacterial resistance and the addition of new antimicrobial medications, the current and appropriate treatment of ocular bacterial infections is an important issue for eye care practitioners. METHODS: The literature on the antimicrobial treatment of ocular bacterial infections is reviewed to provide the practicing optometrist with an overview of the issues and medications involved in therapy. RESULTS: New topical, oral, and parenteral antibiotic medications continuously become available to eye care practitioners. Clinicians must routinely reassess the conventional antimicrobial therapy in light of the drugs available for the treatment of bacterial eye infections. The clinician must be familiar with distinct protocols and medications for the management of different ocular bacterial infections. CONCLUSIONS: Knowledge of the results of controlled antimicrobial studies and a review of standard practices in managing bacterial eye disease can provide the necessary background to help the eye care clinician make appropriate antimicrobial therapeutic decisions in patient care.

Anti-Bacterial Agents↗

PubMed1997

Occurrence of citrus viroids in Costa Rica.

A survey for citrus viroids was conducted in the major citrus commercial growing areas in Costa Rica. Screening of 36 sweet orange and 12 lemon trees resulted in the detection of members of four of the five citrus viroid groups as determined by nucleic acid hybridization using specific RNA probes and polymerase chain reaction (PCR) using specific oligonucleotide primers. CEVd, CVd-IIa, CVD-IIb and CVd-III viroids were found to be widespread in the three main regions of commercial citrus production. CVd-Ib was only found in lemon in Nicoya.

Citrus↗

PubMed1996

RNA structural features responsible for potato spindle tuber viroid pathogenicity.

The native structure of potato spindle tuber viroid (PSTVd) contains a series of short double helices and small internal loops that are organized into five structural domains. Nucleotides within the pathogenicity domain are known to play a critical role in modulating PSTVd symptom expression, and it has been suggested that disruption of a comparatively unstable "premelting region" within the pathogenicity domain may be required for disease induction. We have used a combination of quantitative bioassays, temperature gradient gel electrophoresis of circularized RNA transcripts, and thermodynamic calculations to compare the biological and structural properties of 12 representative PSTVd sequence variants. Certain mutations appeared to act indirectly, downregulating pathogenicity by suppressing the rate of PSTVd replication/accumulation. The effects of other mutations appeared to be more direct, but there was no consistent correlation between symptom severity and melting temperature. Taking into account the three-dimensional shape of RNA helices, comparison of the optimal secondary structures for these variants point to major differences in the geometry of their pathogenicity domains; i.e., variants producing intermediate symptoms possess a linear arrangement of three consecutive helices, whereas for variants producing mild or severe symptoms this domain is bent in opposing directions. Such alterations in RNA structure together with concomitant alterations in RNA-protein interaction(s) may be the primary cause of viroid pathogenicity.

Base Sequence↗

PubMed1996

Fluorescence resonance energy transfer visualization of DNA aggregates formed during electrophoretic separations in ultradilute hydroxyethylcellulose.

Fluorescence resonance energy transfer (FRET) microscopy is used to observe structures of DNA aggregates formed during electrophoresis in ultradilute hydroxyethylcellulose (HEC). FRET gives evidence of aggregates with a tightly packed core and random entanglement of DNA in the outer portions. HEC concentrations also appear to play a role in aggregate formation. DNA aggregates take longer to assemble in higher HEC concentration solutions and assume a less compact form than those formed at lower HEC concentrations.

Cellulose↗

PubMed1996

Extemporaneous preparation of antibiotic ophthalmic solutions.

Until the introduction of ocular ciprofloxacin, the standard of practice in treating bacterial corneal ulcers required topical antibiotic ophthalmic solutions that were either not commercially available or not available in the higher concentrations needed. A survey was mailed to 125 hospital pharmacies and 125 community pharmacies in Oklahoma to determine the availability of extemporaneously prepared antibiotic ophthalmic solutions. Of 72 hospital pharmacies and 60 community pharmacies that responded, 17 hospital and 2 community pharmacies reported that they do compound these solutions. The main reasons given by the other pharmacies for not offering this service were the lack of a laminar flow hood or other equipment and lack of an aseptic environment. If extemporaneously prepared antibiotic ophthalmic solutions are needed to treat corneal ulcers, then pharmacists have a responsibility to prepare them. The recent publication of a handbook providing formulations for those products and the "ASHP Technical Assistance Bulletin on Pharmacy-Prepared Ophthalmic Products" may encourage more pharmacies to provide this needed service.

Administration, Topical↗

PubMed1995

Dynamics of DNA during pulsed field electrophoresis in entangled and dilute polymer solutions.

Using fluorescence video microscopy, DNA electrophoretic behavior under field inversion conditions has been investigated in hydroxyethyl cellulose (HEC) solutions both above and below its entanglement limit. DNA conformational fluctuation periods are found to be strongly influenced by the frequency of the applied electric field. DNA maximum extension is found to be dependent on both the frequency and the strength of the applied field. It is proposed that both above and below the HEC entanglement limit, field inversion serves to keep the average DNA conformation in a size-dependent regime intermediate between full extension and random coil. In this time-averaged geometry, efficient long-chain DNA electrophoretic separation is enabled.

DNA, Fungal↗

PubMed1995

The complete nucleotide sequence of RNA 3 of a peach isolate of Prunus necrotic ringspot virus.

The complete nucleotide sequence of RNA 3 of the PE-5 peach isolate of Prunus necrotic ringspot ilarvirus (PNRSV) was obtained from cloned cDNA. The RNA sequence is 1941 nucleotides and contains two open reading frames (ORFs). ORF 1 consisted of 284 amino acids with a calculated molecular weight of 31,729 Da and ORF 2 contained 224 amino acids with a calculated molecular weight of 25,018 Da. ORF 2 corresponds to the coat protein gene. Expression of ORF 2 engineered into a pTrcHis vector in Escherichia coli results in a fusion polypeptide of approximately 28 kDa which cross-reacts with PNRSV polyclonal antiserum. Analysis of the coat protein amino acid sequence reveals a putative "zinc-finger" domain at the amino-terminal portion of the protein. Two tetranucleotide AUGC motifs occur in the 3'-UTR of the RNA and may function in coat protein binding and genome activation. ORF 1 homologies to other ilarviruses and alfalfa mosaic virus are confined to limited regions of conserved amino acids. The translated amino acid sequence of the coat protein gene shows 92% similarity to one isolate of apple mosaic virus, a closely related member of the ilarvirus group of plant viruses, but only 66% similarity to the amino acid sequence of the coat protein gene of a second isolate. These relationships are also reflected at the nucleotide sequence level. These results in one instance confirm the close similarities observed at the biophysical and serological levels between these two viruses, but on the other hand call into question the nomenclature used to describe these viruses.

Amino Acid Sequence↗

PubMed1995

DNA conformational dynamics in polymer solutions above and below the entanglement limit.

Video microscopy of nucleic acids (DNA) undergoing electrophoresis in hydroxyethyl cellulose (HEC) sieving buffers demonstrates previously unobserved shape-changing interactions between DNA and HEC molecules. We provide the first visual demonstration of entanglement between DNA and one or several discrete HEC molecules, which has been postulated to occur in ultradilute polymer solutions. Typically, nucleic acids appear to become entangled with HEC at a single region only, in both dilute and fully entangled HEC solutions. Fluctuations of the center of mass velocity of a DNA molecule and its correlation with conformation are revealed from analyses of the image data. These observations account for the success of recently reported rapid, high-resolution dc and pulsed-field capillary electrophoretic separations of nucleic acids in ultradilute hydroxyethyl cellulose solutions and hydroxyethyl cellulose/poly(ethylene oxide) solutions.

Cellulose↗

PubMed1994

Agrobacterium-mediated inoculation of PSTVd cDNAs onto tomato reveals the biological effect of apparently lethal mutations.

Potato spindle tuber viroid (PSTVd) mutants which contain alterations in the terminal loops of the rod-like native structure have previously been reported from our laboratory. PSTVd-P contains mutations at positions 2, 4, and 6 in the left terminal loop; PSTVd-R+, a sequence permutation of PSTVd-R, contains the same mutations at positions 177 and 178 in the right terminal loop as PSTVd-R and contains in addition a 1-nucleotide G insertion at position 176. PSTVd-P, PSTVd-R, and PSTV-R+ were noninfectious when either cDNA or SP6-generated RNA transcripts were used as inoculum onto tomato cotyledons. In the current study, mutant and wild-type PSTVd constructs were mobilized into Agrobacterium tumefaciens and used for stem inoculation of tomato plants. Agrobacterium-mediated inoculation of the mutant and wild-type constructs has confirmed the inability of the PSTVd-P mutant to establish an infection. The PSTV-R+ mutant and/or sequence variants derived in vivo can establish an infection, although PSTVd-R+ progeny and replicative intermediates appear to be primarily restricted to the gall and root tissues of the plant and only occasionally are progeny detectable in the newly developing leaves. The reduced level of viroid accumulation from the PSTVd-R+ mutant appears to be consistent with the mutant viroid replicating/accumulating only in a limited number of cells or cell types. The mutations in the right terminal loop may alter interactions with specific host components and thereby disrupt the normal pattern of intercellular transport of the viroid or limit its replication to a cell type but not abolish replication per se.

Agrobacterium tumefaciens↗

PubMed1993

Chemiluminescent detection of potato and pome fruit viroids by digoxigenin-labeled dot blot and tissue blot hybridization.

A chemiluminescent molecular hybridization protocol was compared to 32P autoradiography for detecting potato spindle tuber viroid (PSTVd) and apple scar skin group viroids (ASSVd). Labeled cRNA probes for PSTVd and ASSVd were synthesized by SP6 RNA polymerase transcription using digoxigenin-11-UTP or alpha-[32P]UTP. Dot blot hybridization of purified viroids and sap extracts from infected plants showed that chemiluminescent detection using digoxigenin-labeled probes was as sensitive as autoradiography using 32P probes. A minimum of 2.0-2.5 pg purified viroid was detected. ASSVd could be detected in as little as 0.4 ng of total nucleic acid extract from infected tissue or in sap extracts diluted to 10(-3) with healthy extracts. Tissue blots of PSTVd-infected potato tubers and tomato roots, stems and leaves and ASSVd-infected apple fruit, stems and petioles, gave positive reactions when hybridized with the digoxigenin probe. No reaction with similar tissues from healthy plants was observed.

Digoxigenin↗

PubMed1993

Mechanism of viroid pathogenesis: differential activation of the interferon-induced, double-stranded RNA-activated, M(r) 68,000 protein kinase by viroid strains of varying pathogenicity.

Purified potato spindle tuber viroid (PSTVd) was added to an in vitro assay system containing purified interferon-induced, dsRNA-activated protein kinase (P68). Viroid RNA activated (phosphorylated) the enzyme, although with less efficiency than did the synthetic, perfectly matched poly I-poly C. In binding experiments, RNA transcripts of the intermediate strain of PSTVd were shown to specifically bind to a P68-antibody complex. Activation of the enzyme by a strain of PSTVd that results in severe symptoms in infected tomato plants was at least ten-fold that by the mild strain. Activation by a strain that results in intermediate symptoms was quantitatively similar to activation by the severe strain. To our knowledge, this is the first demonstration of a differential effect of viroid strains inducing different levels of pathology on any biochemical or metabolic system investigated. This differential effect suggests that activation of a plant enzyme homologous to mammalian P68 protein kinase may represent the triggering event in viroid pathogenesis. Differential activation of P68 is surprising, because the primary structures of the mild and severe PSTVd strains analyzed differ by only a two-nucleotide inversion (UUC-->CUU) in the lower portion of the 'pathogenicity' region of the molecules. This change, according to thermodynamic calculations, should have only a minor effect on the secondary structure of the viroid molecule. Binding assays indicated that PSTVd specifically binds to P68.

Animals↗

PubMed1993

Childhood depression and risk of suicide: a preliminary report of a longitudinal study.

In the course of locating a sample of 427 adults who were assessed as children or adolescents with either major depressive disorder, mixed anxiety states, or no psychiatric disorder (normal controls), we found seven cases of suicide. Of the original sample, we located 159 of the 204 subjects with major depressive disorder (78%), 37 of the 66 subjects with anxiety disorders (56%), and 85 of the 177 normal controls (48%). All seven suicides occurred exclusively among the 159 children located from the major depressive disorder group, yielding a rate of 4.4% over approximately 10 years. Psychological autopsy was conducted in the seven suicide victims to assess the psychological status since the initial assessment and at the time of death. Although the onset of the first depressive episode in these victims was around puberty, the suicides usually did not occur until late adolescence or early adulthood. At least five of the seven subjects had recurrent depressive symptoms and were clinically depressed at the time of death. These preliminary findings suggest that major depressive disorder in childhood has significant mortality by suicide.

Adolescent↗

PubMed1993

Viroids: the smallest and simplest agents of infectious disease. How do they make plants sick?

Viroids are autonomously replicating pathogens of higher plants that consist solely of unencapsidated, single-stranded, circular RNAs of 246-375 nucleotides. Despite their extreme simplicity, viroids cause syndromes in plants that are about as varied as those caused by plant viruses. Because viroids are not translated, their effects on plants must be a consequence of direct interaction of the viroid with host constituents. Although the molecular mechanisms of viroid pathogenesis are still unknown, analysis of molecular chimeras between viroids of different pathogenicity levels has revealed that the severity of symptoms is the result of complex interactions among three of the five viroid domains. In vitro experiments with purified mammalian protein kinase P68 have shown that the enzyme is strongly activated (phosphorylated) by viroid strains that incite moderate to severe symptoms, but far less by a mild strain. Activation of a plant homolog of P68 may be the triggering event in viroid pathogenesis.

Base Sequence↗

PubMed1993

The effect of caffeine on the accommodative response/accommodative stimulus function and on the response AC/A ratio.

Using a phoro-accommodometer, accommodation and convergence responses were measured for 17 experimental subjects before and after they ingested 200 mg caffeine. For 16 control subjects accommodation and convergence responses were determined at two test sessions separated by 45 min. For the experimental group, the accommodative response/accommodative stimulus (Ar/As) slope increased 0.05 D/D after ingestion of caffeine, and the response AC/A ratio decreased 3.05 delta/D. The y-intercept of the convergence response/accommodative response increased by 3.7 delta in the experimental group. These changes were statistically significant. For the control group, the differences in Ar/As slope, response AC/A ratio, and convergence response/accommodative response y-intercept between first and second test sessions were not statistically significant.

Accommodation, Ocular↗

PubMed1992

Identification of multiple structural domains regulating viroid pathogenicity.

To investigate the role of individual structural domains in viroid pathogenicity and replication, a series of interspecific chimeras was constructed by exchanging the terminal left (TL) and/or pathogenicity (P) domains between tomato apical stunt (TASVd) and citrus exocortis (CEVd) viroids. All six chimeras tested were replicated stably in tomato, and the symptoms exhibited by infected plants were intermediate between those induced by the parental viroids. Quantitative comparisons of symptom development and progeny accumulation revealed that: (i) the TL domain of TASVd contains a determinant required for appearance of severe veinal necrosis in tomato, (ii) the severe epinasty and stunting characteristic of TASVd requires the presence of its TL and P domains, and (iii) the variable (V) and terminal right (TR) domains comprising the right side of the native structure also play an important role in viroid pathogenicity. Chimeras containing the right side of TASVd accumulated to higher levels early in infection, and infected plants developed more severe symptoms than those whose right halves were derived from CEVd. Although the individual contributions of the TL and P domains to symptom induction could not be completely separated from that of viroid titer, the TL domain appears to exert a greater effect upon symptom severity than does the P domain. The TL, P, V, and TR domains of TASVd and CEVd contain three discrete regions of sequence and/or structural variability that may correspond to the pathogenicity determinants uncovered by our genetic analysis.

Base Sequence↗