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Biomedical subjects

A A Levy

Publications and source records attributed to A A Levy.

At least 37 records · Page 2Linked to original sources
PubMed1996

Binding of Nicotiana nuclear proteins to the subterminal regions of the Ac transposable element.

Specific binding of Nicotiana nuclear protein(s) to subterminal regions of the Ac transposable element was detected using gel mobility shift assays. A sequence motif (GGTAAA) repeated in both terminal regions of Ac, was identified as the protein binding site. Mutation of two nucleotides in this motif was sufficient to abolish binding. Based on a series of competition assays, it is deduced that there is cooperative binding between two repeats, each similar to the GGTAAA motif. The binding protein is probably similar to a previously characterized maize protein which binds to a GGTAAA-containing motif located in the ends of Mutator. Moreover, we show that DNA from Ds1 competes for protein binding to Ac termini, and we show, by sequence analysis, that GGTAAA binding sites are present in the terminal region of Tgm1, Tpn1, En/Spm, Tam3, and Ds1-like elements. This suggests that the binding protein(s) might be involved in the transposition process.

Base Sequence↗
PubMed1994

Chromosome painting in plants: in situ hybridization with a DNA probe from a specific microdissected chromosome arm of common wheat.

We report here on the successful painting of a specific plant chromosome within its own genome. Isochromosomes for the long arm of chromosome 5 of the wheat B genome (5BL) were microdissected from first meiotic metaphase spreads of a monoisosomic 5BL line of the common wheat Triticum aestivum cv. Chinese Spring. The dissected isochromosomes were amplified by degenerate oligonucleotide-primed PCR in a single tube reaction. The amplified DNA was used as a complex probe mixture for fluorescent in situ hybridization on first meiotic metaphase spreads of lines carrying 5BL as a distinctive marker. Hybridization signals were observed, specifically, along the entire 5BL. In some of the cells, labeling was also detected in two bivalents, presumably those of the 5B "homoeologues" (partial homologues) found in common wheat (5A and 5D). The probe also revealed discrete domains in tapetal nuclei at interphase, further supporting the probe's high specificity. These data suggest that chromosome and homoeologous group-specific sequences are more abundant in 5BL than genome-specific sequences. Chromosome-painting probes, such as the one described here for 5BL, can facilitate the study of chromosome evolution in polyploid wheat.

Base Sequence↗
PubMed1991

Molecular analysis of the loss of somatic instability in the bz2::mu1 allele of maize.

Multiple genetic and epigenetic changes were detected within one plant generation at the bz2::mu1 mutable allele in a population of 118 plants. Loss of somatic instability in bz2::mu1 was usually correlated with methylation of the Mu1 transposable element; in 6 plants, somatic instability was lost as a result of mutations in bz2::mu1. This is a surprisingly high frequency of mutation per allele (2.5%) for the Mutator family, for which germinal revertants occur at a frequency of about 10(-4) per gamete. One germinal excision event was found that contained an 8 bp deletion, frameshift mutation in Bronze-2. The three other mutants described occurred as a result of abortive transposition, in which 75-77 bp deletions were generated at the junction between Bronze-2 and Mu1. We discuss the possible mechanisms, and the role of host factors in abortive transposition in maize.

Alleles↗
PubMed1991

Analysis of a 120-kilobase mitochondrial chromosome in maize.

The organization of the mitochondrial genome in plants is not well understood. In maize mitochondrial DNA (mtDNA) several subgenomic circular molecules as well as an abundant fraction of linear molecules have been seen by electron microscopy. It has been hypothesized that the circular molecules are the genetic entities of the mitochondrial genome while the linear molecules correspond to randomly sheared mtDNA. A model has been proposed that explains the mechanism of generation of subgenomic circles (of a predictable size) by homologous recombination between pairs of large direct repeats found on a large (approximately 570 kb for the fertile (N) cytoplasm) master circle. So far the physical entities of the mitochondrial genome, as they exist in vivo, and the genes they carry, have not been identified. For this purpose, we used two gel systems (pulsed field gel electrophoresis and Eckhardt gels) designed to resolve large DNA. Large DNA was prepared from the Black Mexican Sweet (BMS) cultivar. We resolved several size classes of mtDNA circles and designate these as chromosomes. A 120 kb chromosome was mapped in detail. It is shown to contain the three ribosomal genes (rrn26, rrn18 and rrn5) plus two genes encoding subunits of cytochrome oxidase (Cox1 and Cox3); it appears to be colinear with the 570-kb master circle map of another fertile cytoplasm (B37N) except at the "breakpoints" required to form the 120-kb circle. The presence of the 120-kb chromosome could not have been predicted by homologous recombination through any of the known repetitive sequences nor is it a universal feature of normal maize mitochondria. It is present in mitochondria of BMS suspension cultures and seedlings, but is not detectable in seedlings of B37N. No master genome was detected in BMS.

Blotting, Southern↗
PubMed1990

Regulation of the timing of transposable element excision during maize development.

The ability of transposable elements (TEs) to insert into or excise out of a genetic locus can be regulated by genetic, environmental, and developmental factors. Tissue- or organ-specific activity of TEs is a frequent and well-characterized example of spatial, developmental regulation. Regulation of the timing of TE activity during ontogeny is less well understood. To analyze timing, TE-induced variegation was quantified in the aleurone of maize kernels, a tissue composed of only a single layer of cells, and sector sizes were assigned to specific cell divisions in aleurone development. Three TE families, Mu, Spm, and Ac/Ds, were studied at two genetic loci. It was found that the frequency of transposon excision changes drastically (up to 30-fold increase or equivalent decrease) during the proliferation of the aleurone. Moreover, these changes occur at the same cell divisions in all three TE families. These results suggest that the timing of TE excision during maize development can be controlled by the host.

Alleles↗
PubMed1989

Developmental and genetic aspects of Mutator excision in maize.

The regulation of excision of Mu elements of the Mutator transposable element family of maize is not well understood. We have used somatic instability of Mu receptor elements from the Bronze 1 and Bronze 2 loci to monitor the frequency and the timing of excision of Mu elements in several tissues. We show that spot size in the aleurone of a bz2::mu1 stock varies between one to approximately 256 cells. This indicates that excision events begin eight divisions prior to full aleurone differentiation and end after the last division of the aleurone. We show that excision is equally biased for late events in all other tissues studied. A locus on chromosome 5 has been identified that affects spot size, possibly by altering the timing of Mu excision. Using somatic excision as an assay of Mutator activity, we found that activity can change in small sectors of the tassel; however, there are no overall activity changes in the tassel during the period of pollen shedding. We also report the recovery of germinal revertants for the bz1::mu1 and bz2::mu1 alleles. One of these revertant alleles was characterized by Southern blot analysis and found to be similar to the progenitor of the mutable allele.

Alleles↗
PubMed1986

Gene-dosage compensation of endosperm proteins in hexaploid wheat Triticum aestivum.

Several aneuploid lines and one intervarietal substitution line of the hexaploid wheat Triticum aestivum (2n = 6x = 42; genomes AABBDD) cv. Chinese Spring were used to study the effects of different doses of chromosomes 1B, 1D, or 1A on the amount of the high molecular weight ("HMW") glutenins and gliadins of endosperm. These homeologous chromosomes carry HMW glutenin and gliadin gene clusters on their long and short arms, respectively. Increasing the dosage of chromosome 1B of Chinese Spring in plants having in their 3n endosperm zero or the normal three doses of the homeologue 1D, as well as in plants carrying in their endosperm one dose of 1B of the cultivar Timstein, had a dual effect: on one hand, a nonlinear increase in the amount of each subunit encoded by the chromosome whose dosage was elevated and, on the other hand, a compensating nonspecific decrease in the amount of other HMW glutenin and gliadin subunits encoded either by the homeoalleles on 1D or by the homoalleles on 1B of Timstein, respectively. Deletion of chromosome arm 1BL, which carries only a few HMW glutenin genes, had no significant effect on the amount of HMW glutenins encoded by 1DL and HMW gliadins encoded by 1DS and 1BS. However, deletion of 1BS or 1DS, each carrying many gliadin genes, caused a significant but nonspecific increase in the HMW glutenins and gliadins encoded by the remaining arms of 1B and 1D. The possible mechanism and evolutionary implications of gene-dosage compensation in polyploid wheat are discussed.

Journal Article↗
PubMed1976

Changes in plasma potassium and calcium levels and in the electrocardiogram after a single dose of succinylcholine preceded by d-tubocurarine.

One hundred and eighteen patients undergoing surgical procedures not requiring immediate tracheal intubation, nor producing visceral reflexes, were pretreated with d-tubocurarine 6 mg, three minutes before the administration of a bolus of succinylcholine (2 mg/kg). Electrocardiographic changes, venous and arterial plasma potassium and calcium levels, CPK changes (12 patients) and appearance of myoglobinuria (35 patients) were followed. Pretreatment with a small dose of d-tubocurarine did not change the overall incidence and pattern of arrhythmias; it did, however, prevent increases in plasma potassium in 90.4 per cent of the patients, mean plasma potassium values remaining below pre-induction levels. The CPK level changed in only one of 12 patients (from 10 to 21 I.U., the normal range being 0 to 34 I.U.). No myoglobinuria was detected in any of the patients tested. A rapid but short-lasting change in the K+/Ca++ ratio did not seem to influence the occurrence of arrhythmias. Pretreatment with a small dose of d-tubocurarine is effective in preventing or decreasing fasciculations, plasma potassium and CPK changes and myoglobinuria described after the intravenous administration of succinylcholine. The already useful role of succinylcholine in our armamentarium can be made safer by pretreatment with a small dose of d-tubocurarine.

Adolescent↗
PubMed1975

Uptake of local anaesthetics: movement of ethanol into frog sciatic nerve.

The changes of nerve action potential with time of the excised bullfrog sciaticperoneal nerve were measured at 24 degrees C with the nerve immersed in oxygenated mineral oil containing various concentrations of ethanol. One series of measurements was made with intact nerve and a range of about 20 to 110 millimolar ethanol. Another series was made with nerves in which the epineural sheath was cut open longitudinally and using a range of about 15 to 51 millimolar ethanol. The results were analysed by means of simple diffusion theory, and below applied ethanol concentrations of about 70 millimolar the latent periods and times to total block fitted the theoretical pattern well. Disagreements between theory and measurement of previous workers is explainable by their neglecting to recognize that nerve bundles do not extend to the nerve periphery. It was found that the minimum oil concentration of ethanol capable of producing total block is 15 millimolar. Above 70 millimolar, behaviour was observed consistent with nerve damage. It was found possible, by measuring the ratio latent period: time to total block, to separate the relative contribution of the epineural sheath and epineurium as a diffusion barrier to ethanol from that of the perineurium and perilemma.

Action Potentials↗