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W F Thompson

Publications and source records attributed to W F Thompson.

At least 73 records · Page 4Linked to original sources
PubMed1986

Phytochrome Control of Specific mRNA levels in Developing Pea Buds : Kinetics of Accumulation, Reciprocity, and Escape Kinetics of the Low Fluence Response.

We have examined the time course for accumulation of each of 12 different nuclear gene transcripts in pea buds after irradiating dark grown seedlings with a single pulse low fluence red light (10(3) micromoles per square meter delivered in 100 seconds). The 12 time courses can be grouped into four general classes. Six transcripts (including RNAs coding for the chlorophyll a/b binding protein and ribulose-1,5-bisphosphate carboxylase) accumulate at a linear rate during 24 hours in darkness following the light pulse. Two transcripts increase rapidly at first but then reach a plateau after 3 hours and remain at that level for the next 21 hours. Another two transcripts exhibit a prolonged lag period before beginning to accumulate, and do not reach significant accumulation rates until 12 to 16 hours after the red light pulse. One transcript appears to undergo a transient increase in abundance in response to red light, but this is superimposed on a background of slowly increasing abundance of this RNA in control plants. This response, unlike all the others, exhibits reciprocity failure in experiments in which the same fluence of light is given over periods ranging between 50 and 4000 seconds.We have also examined the kinetics with which each of these 12 responses escapes from phytochrome-far-red absorbing form control by attempting to reverse the induction with far-red light given at various times after the red light pulse. Again, several different patterns are apparent for the different transcripts. The time at which far red reversibility first begins to be lost, the rate at which it is lost, and the final extent of reversibility remaining after 7 hours in the dark all differ for different transcripts. In addition, we have observed that some responses retain virtually complete photoreversibility for at least 7 hours. In some cases, a comparison of the time course and escape kinetic data indicates that relatively rapid turnover of the RNA must occur. It is not clear whether or not the rate of turnover is influenced by phytochrome.

Journal Article↗
PubMed1986

Occult spinal dysraphism. Case report and review of the literature.

This case report and review of the literature is presented to create a greater diagnostic awareness of occult spinal dysraphism. Early recognition is based upon an understanding of this congenital anomaly and its variable presentations. These most commonly include abnormal gait, various cutaneous manifestations, particularly subcutaneous lipomata, and less frequently urological complaints. Surgical intervention, to arrest disease progression, is the primary mode of treatment, and functional improvement is variable. Long-term prognosis is dependent upon severity of neurologic deficits prior to surgery and the type of lesion found intraoperatively. Familial occurrence has been reported and genetic counseling may be an important preventive measure. Recent radiologic investigations have been concerned with the use of ultrasonography in screening infants at risk.

Child↗
PubMed1985

Inheritance, organization, and mapping of rbcS and cab multigene families in pea.

DNA restriction endonuclease fragment patterns corresponding to both the rbcS and cab multigene families of pea are each shown to segregate as single Mendelian units in the F(2) progeny of two separate crosses. All of the observed variation in each of the multigene families is thus organized on the chromosome in a tightly linked complex. Linkage relationships between both multigene families and an array of morphological and isozyme markers establish the location of the rbcS and cab gene clusters on pea chromosomes 5 and 2, respectively. Our results, which indicate a high level of DNA restriction fragment length polymorphism in pea, suggest sufficient variation to permit the construction of a highly detailed linkage map.

Journal Article↗
PubMed1985

Phytochrome control of specific mRNA levels in developing pea buds : the presence of both very low fluence and low fluence responses.

We have examined phytochrome regulated changes in transcript abundance for 11 different light regulated mRNAs in developing pea buds. Fluence-response curves were measured for changes in transcript abundance in response to red light pulses in both the low and very low fluence ranges. Most transcripts show only low fluence responses, with a threshold of approximately 10 micromoles per square meter. All of the low fluence responses are reversible by far red light. One transcript shows a very low fluence response, with a threshold of approximately 10(-4) micromoles per square meter. As expected, the very low fluence response is not far red reversible and in fact can be induced by far red light.Various fluences of red light were also used as pretreatments before transferring seedlings to continuous white light. One transcript responds to pretreatments in the very low fluence range, several respond to pretreatments in the low fluence range (including chlorophyll a/b binding protein RNA and ribulose-1,5-bisphosphate carboxylase RNA), and several show no response to the red light under these conditions. The threshold of these low fluence responses is approximately 10(2) micromoles per square meter, one order of magnitude greater than the threshold of the low fluence responses to red light alone.The transcripts may also be grouped by their responses to white light treatment alone. Three of the clones correspond to transcripts whose abundance decreases after a 24 hour white light treatment. The remainder of the mRNAs increase between 2- and 10-fold in response to the 24 hour white light.

Journal Article↗
PubMed1985

Distortion of H2-antagonist equilibrium constants by uptake in rabbit gastric mucosal cells.

In rabbit gastric cells the new H2-antagonists, BL-6341A, SK&F 93479 and L-643,441 were highly potent inhibitors of the H2-receptor mediated action of histamine as monitored by 14C-aminopyrine uptake and cyclic AMP formation. BL-6341A and SK&F 93479 acted as competitive antagonists to histamine and dimaprit but they were less potent against dimaprit (Ki, 8.9 nM) than against histamine (Ki, 3.5-4.4 nM). Furthermore, the Schild slope for L-643,441 against histamine was significantly higher than unity (1.69-1.79), which is inconsistent with competitive antagonism, whereas against dimaprit it was close to unity. In contrast to these antagonists, cimetidine was an equally potent competitive antagonist of both histamine and dimaprit. 3H-histamine was taken up by gastric cells as evidenced by the loss of 60-70% of the cell-associated radioactivity upon hypotonic lysis. These results suggest that uptake and possibly metabolism of histamine by rabbit gastric cells is partially responsible for the distortion of the estimated equilibrium constants for these H2-antagonists.

Aminopyrine↗
PubMed1983

DNase I sensitivity of transcriptionally active genes in intact nuclei and isolated chromatin of plants.

We have investigated the DNase I sensitivity of transcriptionally active DNA sequences in intact nuclei and isolated chromatin from embryos of wheat (Triticum aestivum L.). Nuclei or isolated chromatin was incubated with DNase I, and the extent of DNA digestion was monitored as percentage acid solubility. The resistant DNA and DNA from sham-digested controls were used to drive reassociation reactions with cDNA populations corresponding to either total poly(A)+RNA from unimbibed wheat embryos or polysomal poly(A)+RNA from embryos that had imbibed for 3 hr. Sequences complementary to either probe were depleted in DNase I-resistant DNA from nuclei and from chromatin isolated under low-ionic-strength conditions. This indicates that transcriptionally active sequences are preferentially DNase I sensitive in plants. In chromatin isolated at higher ionic strength, cDNA complementary sequences were not preferentially depleted by DNase I treatment. Therefore, the chromatin structure that confers preferential DNase I sensitivity to transcriptionally active genes appears to be lost when the higher-ionic-strength method of preparation is used. Treatment of wheat nuclei with DNase I causes the release of four prominent nonhistone chromosomal proteins that comigrate with wheat high mobility group proteins on NaDodSO4 gels.

Cell Nucleus↗
PubMed1982

Novel evolutionary variation in transcription and location of two chloroplast genes.

We have found major evolutionary changes in the types of transcripts produced by specific chloroplast genes, in particular those encoding the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase and a photosystem II polypeptide (PII). Two distinct patterns of LS gene transcripts are revealed by hybridizing an LS gene probe to electrophoretically separated RNA from 19 angiosperms. Most species, including pea, contain the single transcript of approximately 1.6 kb previously observed in corn, spinach and mustard. However, in mung bean and other members of the legume genera Vigna and Phaseolus, the 1.6 kb transcript represents only a minor fraction of LS transcripts, and instead, two larger LS transcripts of approximately 2.4 and 2.6 kb predominate. The PII gene produces a single transcript in pea and most other species examined, while members of the related legume genera Vigna, Phaseolus and Glycine contain two additional transcripts which are smaller in size and probably represent specific RNA breakdown products. A single species, sweet pea (Lathyrus odoratus), contains a second PII transcript which is 0.2 kb larger than the approximately 1.2 kb transcript found in all species. The LS and PII genes map to the same 5 kb region in both pea and mung bean and are transcribed off the same DNA strand. In contrast, published studies indicate that the two genes are approximately 50 kb apart and are transcribed off opposite DNA strands in five other chloroplast genomes. These differences are probably the consequence of an approximately 50 kb inversion which distinguishes the pea and mung bean genomes from those of most other angiosperms (1).

Biological Evolution↗
PubMed1982

Secretion of intrinsic factor from dispersed mucosal cells isolated from guinea pig and rabbit stomach.

In dispersed mucosal cells prepared from rabbit and guinea pig stomach, the secretion of intrinsic factor was constant (0.3-0.4%/min) for at least 30 min incubation at 37 degrees C. Histamine or isobutyl methylxanthine increased cyclic AMP and intrinsic factor secretion in both cells preparations. Isobutyl methylxanthine potentiated and cimetidine competitively inhibited (ki = 5.10-7 M) both effects of histamine. Dibutyryl cyclic AMP (1.0 mM), also caused a 3-fold increase in intrinsic factor secretion. These results suggest that in rabbit and guinea pig histamine interacts with H2-receptors to increase cyclic AMP which mediates the rise in the rate of intrinsic factor secretion.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Chloroplast DNA rearrangements are more frequent when a large inverted repeat sequence is lost.

We examined the arrangement of sequences common to seven angiosperm chloroplast genomes. The chloroplast DNAs of spinach, petunia and cucumber are essentially colinear. They share with the corn chloroplast genome a large inversion of approximately 50 kb relative to the genomes of three legumes--mung bean, pea and broad bean. There is one additional rearrangement, a second, smaller inversion within the 50 kb inversion, which is specific to the corn genome. These two changes are the only detectable rearrangements that have occurred during the evolution of the species examined (corn, spinach, petunia, cucumber and mung bean) whose chloroplast genomes contain a large inverted repeat sequence of 22-25 kb. In contrast, we find extensive sequence rearrangements in comparing the pea and broad bean genomes, both of which have deleted one entire segment of the inverted repeat, and also in comparing each of these to the mung bean genome. Thus there is a relatively stable arrangement of sequences in those genomes with the inverted repeat and a much more dynamic arrangement in those that have lost it. We discuss several explanations for this correlation, including the possibility that the inverted repeat may play a direct role in maintaining a conserved arrangement of chloroplast DNA sequences.

Base Sequence↗
PubMed1981

Evolutionary sequence divergence within repeated DNA families of higher plant genomes. I. Analysis of reassociation kinetics.

The higher proportion of repeated DNA sequences in the garden pea (Pisum sativum) than in the mung bean (Vigna radiata), as well as other differences between these legume genomes, are consistent with a higher rate of sequence amplification in the former. This hypothesis leads to a prediction that repeated sequence families in Pisum are mostly heterogeneous, as defined by Bendich and Anderson (1977), while Vigna families are homogeneous. An assay developed by these authors to distinguish between the two types of families, by comparison of reassociation rates at different temperatures, was utilized. The results for Vigna defied the predictions of the assay for either homogeneous or heterogeneous model. Evaluation of the kinetic data in light of the great diversity of repeated family copy numbers in both genomes enabled an interpretation of the results as consistent with heterogeneous families in Pisum and homogeneous families in Vigna. These tentative conclusions were supported by the results of a thermal denaturation (melting) assay described in the accompanying paper.

Biological Evolution↗
PubMed1981

Evolutionary sequence divergence within repeated DNA families of higher plant genomes. II. Analysis of thermal denaturation.

An assay based on derivative analysis of thermal denaturation (melting) behavior of reassociated DNA was developed in an attempt to characterize the sequence relationships in repeated DNA families according to the homogeneous or heterogeneous models of Bendich and Anderson (1977). The validity of the technique was confirmed by the use of deaminated Escherichia coli DNA models for repetitive families. The melting data for DNA reassociated at two different temperatures provided strong evidence that Pisum sativum repeated families are mostly heterogeneous, while homogeneous families predominate in Vigna radiata. These findings, together with other differences between the two genomes, suggest that the rate of sequence amplification has been higher in the evolutionary history of Pisum DNA. A general trend seems to exist for high amplification rates in large, highly repetitive plant genomes such as Pisum and lower rates in smaller plant genomes such as Vigna, as well as in the generally smaller, less repetitive genomes of most animal species.

Biological Evolution↗
PubMed1981

Clone banks of the mung bean, pea and spinach chloroplast genomes.

All but one of the PstI restriction fragments from mung bean, pea, and spinach chloroplast DNAs have been stably cloned into pBR322. Large fragments (15-54 kb) were cloned at low efficiencies which decreased with increasing fragment length. However, plasmids containing fragments above 25-30 kb were too unstable to be useful. In particular, pBR322 derivatives containing the largest mung bean and spinach fragments (34 kb and 54 kb, respectively) are extremely unstable and rapidly delete parts of the plasmid sequence. The PstI fragments of mung bean chloroplast DNA which cover the 34-kb PstI fragment have been cloned into pACYC177. After a search of several thousand recombinants we were unable to recover a clone containing a 12.2-kb pea chloroplast PstI fragment and suggest that some property of its sequence may be inimical to the cloning process. The identity of the cloned fragments to native chloroplast DNA restriction fragments is demonstrated by restriction analysis and the ability to construct detailed restriction maps of the mung bean and pea chloroplast genomes.

Base Sequence↗
PubMed1981

Rearrangements in the chloroplast genomes of mung bean and pea.

We have mapped all the cleavage sites for the restriction endonucleases BstEII, Kpn I, Pst I, Pvu II, Sac I, Sal I, Sma I, and Xho I on the circular chloroplast chromosomes from mung bean and pea. The mung bean chloroplast genome measures 150 kilobase pairs (kb) in length; it includes two identical sequences of 23 kb that contain the ribosomal genes and are arranged as an inverted repeat separated by single-copy regions of 21 and 83 kb. The pea chloroplast genome is only 120 kb in size, has only one set of ribosomal genes, and does not possess any detectable repeated sequences. The mung bean inverted repeat structure is common to all other nonleguminous higher plant chloroplast genomes studied, whereas the pea structure has been found only in the closely related legume Vicia faba. We conclude from these data that loss of one copy of the inverted repeat sequence has occurred only rarely during the evolution of the Angiosperms, and in the case of the legumes after the divergence of the mung bean line from the pea-Vicia line. We present hybridization data indicating that rearrangements that change the linear order of homologous sequences within the chloroplast genome have been quite frequent during the course of legume evolution.

Journal Article↗
PubMed1980

Rapid isolation of high molecular weight plant DNA.

A method is presented for the rapid isolation of high molecular weight plant DNA (50,000 base pairs or more in length) which is free of contaminants which interfere with complete digestion by restriction endonucleases. The procedure yields total cellular DNA (i.e. nuclear, chloroplast, and mitochondrial DNA). The technique is ideal for the rapid isolation of small amounts of DNA from many different species and is also useful for large scale isolations.

DNA↗
PubMed1979

Studies on DNA sequences in the Osmundaceae.

Phylogenetic relationships of Osmunda cinnamomea, O. claytoniana, and O. regalis were explored by means of DNA sequence comparisons. Hydroxyapatite thermal elution profiles of self-reassociated repetitive DNA fragments were very similar, indicating the absence of gross differences in the amount of recent amplification or addition of repetitive DNA in any of these three genomes. Interspecific DNA sequence comparisons showed, in contrast to our earlier interpretation, that repeated DNA sequences of O. claytoniana are nearly equally diverged from those of O. cinnamomea and O. regalis. Differences between repetitive sequences of the three species can be interpreted as reflecting amplification events which occurred subsequent to speciation. The data obtained suggest that the three Osmunda species most likely arose more or less simultaneously from a common ancestor. These findings were verified in experiments with tracer DNA preparations enriched for single copy sequences. On the basis of the hydridization data presented here and of the fossil record, the rate of single copy sequence divergence in the ferns is comparable to that in the primates, although slower than that observed in other animal taxa. From this first evaluation of rates of DNA evolution in plants it would seem that the rates for plants and animals are roughly comparable. The evidence suggests that species divergence is accompanied by further reiteration of preexisting repeat sequences. The rate of addition of repetitive sequences probably is slower in ferns than in angiosperms. This difference might be attributable to the much larger effective generation time in ferns.

Base Sequence↗