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W F Thompson

Publications and source records attributed to W F Thompson.

79 records · Page 5Linked to original sources
PubMed1978

DNA sequence organization in the pea genome.

The reassociation kinetics of pea (Pisum sativum L.) DNA fragments (300 nucleotides) were measured with hydroxylapatite. The most slowly reassociating fragments do so with a rate constant of 2 X 10(-4) L mol-1s-1, as determined from experiments with total DNA as well as with a tracer enriched for slowly renaturing sequences. This rate is about 1000 times slower than that observed for Escherichia coli DNA included as an internal kinetic standard, indicating a kinetic complexity of 4.5 X 10(9) nucleotide pairs or 4.6 pg of DNA per haploid nucleus. This estimate is in good agreement with previous chemical and cytophotometric measurements. The majority (85%) of the 300 nucleotide fragments contain repetitive sequences. While the reassociation of repetitive DNA could be modeled with two theoretical second-order components, the data did not specify a unique solution. The reassociation kinetics of isolated high- and low-frequency fractions indicate that repetitive sequence families in pea DNA probably cover a broad range of frequencies ranging from 100 to 10 000 or more copies per haploid genome. Single-copy sequences account for about 30% of the DNA, but because of extensive interpersion of repetitive sequences only about 15% of 300 nucleotide fragments reassociate with single-copy kinetics. From studies of hydroxylapatite binding as a function of fragment length, we conclude that the major class of single-copy sequences has a modal length of about 300 nucleotides. Long tracer reassociation kinetics indicate that sequences with an apparent repetition frequency of about 10 000 copies are interspersed at intervals of less than 1300 nucleotides throughout 75% of the genome. At a detection limit of about 3%, we find no single-copy sequences longer than 1000 nucleotides.

DNA↗
PubMed1978

Application of higher derivative techniques to analysis of high-resolution thermal denaturation profiles of reassociated repetitive DNA.

We have analyzed high-resolution denaturation profiles of reassociated repetitive DNA sequences by using a combination of higher derivative analysis and curve-fitting techniques. Procedures originally used for resolution of components in complex absorption spectra were found to be applicable to high-resolution analysis of melting profiles of reassociated repetitive DNA sequences from pea DNA. Under conditions that eliminate the base composition effect on thermal stability (2.4 M tetraethylammonium chloride), such an anlysis can distinquish "thermal classes" of repetitive DNA duplexes exhibiting different amounts of base pair mismatch. Only a single thermal class is observed in reassociated Escherichia coli DNA whereas at least five classes can be reproducibly distinguished in pea and mung bean DNAs.

Base Sequence↗
PubMed1976

Aggregate formation from short fragments of plant DNA.

Large aggregates have been observed after partial reassociation of pea (Pisum sativum L.) DNA preparations sheared to mean single strand fragment lengths as short as 350 nucleotides. At high DNA concentrations and conditions of salt and temperature which require only moderate precision of base pairing, aggregates pelletable by brief centrifugation account for 30 to 40% of the total DNA from peas, while calf thymus DNA reassociated under similar conditions forms less than 10% pelletable structures. In contrast to networks formed during the reassociation of long DNA fragments containing interspersed repetitive sequences, these aggregates contain a high percentage of double-stranded DNA and are enriched in repetitive sequences.Aggregates detectable by centrifugation do not begin to appear until after extensive repetitive sequence reassociation has already occurred. The results are consistent with a model involving secondary reassociation between single-stranded regions ("hanging tails") remaining after initial duplex formation. This process would lead to formation of large multimers of the original fragments, analogous to the large hyperpolymers which have been observed in extensively reassociated prokaryotic DNA. Randomly sheared fragments containing short (about 300 base pairs) repetitive sequences interspersed with single copy DNA would not be expected to hyperpolymerize significantly under these conditions. I suggest, as a working hypothesis, that much of the repetitive sequence DNA in peas is contained in regions considerably longer than 300 base pairs.

Journal Article↗
PubMed1972

Effect of light and gibberellin on ribonucleic Acid species of pea stem tissues as studied by deoxyribonucleic Acid-ribonucleic Acid hybridization.

The ability of gibberellin and light to alter gene transcription in dwarf pea (Pisum sativum L., var. Progress No. 9) stem issues has been investigated by means of DNA/RNA hybridization-competition techniques. Distinct changes in hybridizable RNA are caused by a 24-hour pretreatment of the seedlings with light, but no changes in RNA were detected up to 50 hours after treatment of the seedlings with gibberellin. Gibberellin is similar to auxin in its ability to induce stem growth without causing detectable changes in hybridizable RNA.

Journal Article↗
PubMed1971

Auxin and ribonucleic Acid synthesis in pea stem tissue as studied by deoxyribonucleic Acid-ribonucleic Acid hybridization.

The ability of auxin to alter gene transcription in pea (Pisum sativum L.) stem tissues has been investigated by means of DNA/RNA hybridization-competition techniques. In order to obtain reproducible hybridization with total nucleic acid preparations from plants it was found necessary to remove interfering substances, probably polysaccharides; this was accomplished by methoxyethanol extraction and precipitation with cetyltrimethylammonium bromide. When purified in this fashion, plant nucleic acids could be made to form hybrids which showed both species specificity and high thermal stability.No change in hybridizable RNA of stem sections in response to auxin could be detected over a 2- to 24-hour period, regardless of the auxin level employed. In contrast, when large doses of auxin were applied to intact pea seedlings, definite changes in the hybridizable RNA of stem tissue were detected both 8 and 24 hours after treatment. Many of the 2,4-D-induced species of RNA which were present at 24 hours were also present at 8 hours. Sections apparently lack a factor needed for the manifestation of the auxin effect on RNA synthesis.Since the hybridization assay employed does not measure all cellular RNA, it is still possible that certain RNA species may be synthesized in sections in response to auxin. However, the auxin promotion of cell elongation in such sections is clearly not associated with changes in hybridizable RNA such as have been reported for several hormonal responses in animal systems.

Journal Article↗