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Biomedical subjects

R J Britten

Publications and source records attributed to R J Britten.

At least 163 records · Page 9Linked to original sources
PubMed1976

Studies on nucleic acid reassociation kinetics: empirical equations describing DNA reassociation.

The rate of appearance of duplex DNA renaturation, measured with single strand specific nuclease, deviates significantly from a second order reaction. Measurements reported in paper I of this series indicate an inhibition in the rate of reassociation of single strand tails on partially reassociated molecules by a factor of at least two. Equations are derived that describe the observed form of reassociation kinetics as measured with hydroxyapatite and with single strand specific nuclease. The free parameter that describes the extent of inhibition of nucleation with single strand tails in these equations has been evaluated by least squares methods and agrees with the experimentally measured value.

Base Sequence↗
PubMed1976

DNA sequence organization in the lepidopteran Antheraea pernyi.

A large fraction of the genome of the lepidopteran Antheraea pernyi consists of interspersed single-copy sequences and repetitive DNA sequences of 300 nucleotide average length. Most of the single-copy sequences are about 800 nucleotides long and a minority are considerably longer. Thus, the organization of the DNA sequences of this insect is similar to that of most higher organisms and different from that of Drosophila.

Animals↗
PubMed1976

DNA sequence arrangement and preliminary evidence on its evolution.

Some recent measurements of the sequence arrangement and evolution of the eukaryotic genome are reviewed. The range of genome sizes and extent of sequence transcribed into nuclear and messenger RNA indicate that the majority of the single copy DNA is not made up of structural genes. The rate of base substitution in the single copy DNA among the primates is similar to that of the codons for certain rapidly changing amino acid residues. This leads to the hypothesis that there is a "basal" rate of change in the genome not strongly affected by selection. The DNA of most higher animals shows a large amount of short period interspersion of repetitive and single copy DNA sequences and a smaller amount of long repetitive regions. The sequence divergence among the short interspersed repetitive sequences is greater than that of the sequences in long repetitive regions. The long repetitive regions are most probably recent additions to the genome and the short interspersed repetitive sequences result from a history of base substitution and translocation. The process of sequence rearrangement appears to be a significant part of the evolution of the genome and may have a much greater effect on the evolution of the phenotype than sequence alteration by base substitution.

Alleles↗
PubMed1975

DNA sequence organization in the genomes of five marine invertebrates.

The arrangement of repetitive and non-repetitive sequence was studied in the genomic DNA of the oyster (Crassostrea virginica), the surf clam (Spisula solidissima), the horseshoe crab (Limulus polyphemus), a nemertean worm (Cerebratulus lacteus) and a jelly-fish (Aurelia aurita). Except for the jellyfish these animals belong to the protostomial branch of animal evolution, for which little information regarding DNA sequence organization has previously been available. The reassociation kinetics of short (250-300 nucleotide) and long (2,000-3,000 nucleotide) DNA fragments was studied by the hydroxyapatite method. It was shown that in each case a major fraction of the DNA consists of single copy sequences less than about 3,000 nucleotides in length, interspersed with short repetitive sequences. The lengths of the repetitive sequences were estimated by optical hyperchromicity and S1 nuclease measurements made on renaturation products. All the genomes studied include a prominent fraction of interspersed repetitive sequences about 300 nucleotides in length, as well as longer repetitive sequence regions.

Animals↗
PubMed1975

Comparative aspects of DNA organization in Metazoa.

Data on sequence organization in metazoa are reviewed and tabulated. It is shown that the features of sequence organization previously observed in Xenopus DNA are extremely widespread. At least 70% of DNA fragments 2,000-3,000 nucleotides long contain both single copy and repetitive sequence in all the organisms examined except Drosophila.

Animals↗
PubMed1975

DNA sequence organization in the mollusc Aplysia californica.

The sequence organization of the DNA of the mollusc Aplysia californica has been examined by a combination of techniques. Close-spaced interspersion of repetitive and single copy sequences occurs throughout the majority of the genome. Detailed examination of the DNA of this protostome reveals great similarities to the pattern observed in the two deuterostome organisms previously examined in detail in this laboratory, Xenopus laevis and Strongylocentrotus purpuratus. Labeled and unlabeled Aplysia DNA were prepared from developing embryos and sheared to a fragment length of 400 nucleotides. The kinetics of reassociation were studied by means of hydroxyapatite chromatography, single-strand-specific S1 nuclease, and optical methods of assay. Aplysia DNA of this fragment length contains at least five resolvable kinetic fractions. One classification of these fractions, listed with their reassociation rate constants (l M-1 sec-1) is: single copy (0.00057), slow (0.047), fast (2.58), very fast (4000), and foldback (greater than 10(5)). Sequence arrangement was deduced from: the kinetics of reassociation of DNA fragments of length 400 or 2000 nucleotides; the hyperchromicity of reassociated fragments containing duplex regions; the size of duplex regions resistant to S1 nuclease; and the reassociation of labeled fragments of various lengths with short driver fragments. More than 80% of the single copy DNA sequences are interspersed with repetitive sequences. The maximum spacing of the repeats is about 2000 nucleotides, and the average less than 1000. The very fast fraction does not show interspersion with single copy sequences or with other kinetic fractions. The foldback fraction sequences are fairly widely interspersed. The slow fraction sequences are interspersed with the fast fraction, and possibly also with the single copy DNA. The fast fraction is the dominant interspersed repetitive fraction. Its sequences are adjacent to the great majority of the single copy sequences and have an average length of about 300 nucleotides.

Animals↗
PubMed1975

Sequence complexity of heterogeneous nuclear RNA in sea urchin embryos.

The sequence complexity of heterogeneous nuclear RNA is sea urchin gastrulas was measured by RNA-driven hybridization reactions with nonrepetitive sea urchin DNA. 28.5% of the sequence complexity of the genome is represented in the nuclear RNA. This amounts to 1.74 X 10(8) nucleotides of diverse sequence, more than 10 times the nucleotide complexity of the polysomal messenger RNA extracted from sea urchin embryos at the same stage. The complex set of nuclear RNA sequences driving this hybridization reaction was shown to be the same as the rapidly labeled hnRNA, using pulse-labeled nuclear RNA as driver.

Animals↗
PubMed1975

Structural genes adjacent to interspersed repetitive DNA sequences.

The observation that repetitive and single copy sequences are interspersed in animal DNAs has suggested that repetitive sequences are adjacent to single copy structural gene sequences. To test this concept, single copy DNA sequences contiguous to interspersed repetitive sequences were prepared from sea urchin DNA by hydroxyapatite fractionation (repeat-contiguous DNA fraction). These single copy sequences included about one third of the total nonrepetitive sequence in the genome as determined by the amounts recovered during the hydroxyapatite fractionation and by reassociation kinetics. 3H-labeled mRNA from sea urchin gastrula was prepared by puromycin release from polysomes and used in DNA-driven hybridization reactions. The kinetics of mRNA hybridization reactions with excess whole DNA were carefully measured, and the rate of hybridization was found to be 3-5 times slower than the corresponding single copy DNA driver reassociation rate. The mRNA hybridized with excess repeat-contiguous DNA with similar kinetics relative to the driver DNA. At completion 80 percent of that mRNA hybridizable with whole DNA (approximately 65 percent) had reacted with the repeat-contiguous DNA fraction (50 percent). This result shows that 80-100 percent of the mRNA molecules present in sea urchin embryos are transcribed from single copy DNA sequences adjacent to interspersed repetitive sequences in the genome.

Animals↗
PubMed1975

Studies on nucleic acid reassociation kinetics: reactivity of single-stranded tails in DNA-DNA renaturation.

The reassociation kinetics of Escherichia coli DNA were measured by S1 nuclease resistance and hydroxyapatite binding. While the reaction assayed by hydroxyapatite displays second order kinetics, the S1 nuclease measurements follow a non-second order from, as previously reported by Morrow (Ph.D. Dissertation, Stanford University. 1974). Much of the reaction measured with S1 nuclease occurs between single stranded regions of fragments already bearing duplex structures from previous collisions, and between such regions and totally free single strands. Experimental determinations indicate that the nucleation rate of single stranded regions on fragments also containing duplexes is inhibited by an average factor of 2 to 4.

Binding Sites↗
PubMed1974

Distribution of repetitive and nonrepetivite sequence transcripts in HeLa mRNA.

Polyadenylated messenger RNA extracted from HeLa cells was hybridized with a mass excess of HeLa DNA. The kinetics of the hybridization reaction demonstrated that most of the messenger RNA is transcribed from nonrepetitive DNA. The amount of messenger RNA hybridized to DNA was measured both with and without prior RNase treatment. Comparison of the results indicates that within the limits of detection, HeLa messenger RNA does not contain repetitive sequence elements covalently linked to nonrepetitive sequence transcripts. However, a small fraction of the HeLa messenger RNA preparation is transcribed entirely from repetitive DNA sequences. This fraction represents about 6% of the total polyadenylated messenger RNA preparation.

Adenosine↗
PubMed1973

Nonrepetitive DNA sequence representation in sea urchin embryo messenger RNA.

Messenger RNA was prepared from developing sea urchin gastrulae by puromycin release from polyribosomes. Approximately 60% of the total mRNA radioactivity of the postnuclear supernatant was recovered and shown to be free of any other labeled RNA species such as ribosomal and nuclear RNA. The mRNA was examined by hybridization to DNA present in great excess. The mRNA hybridizes almost exclusively with nonrepetitive DNA. Almost all of the messenger RNA molecules of sea urchin gastrulae therefore consist of transcripts from nonrepetitive sequences. It appears that the structural genes expressed at this stage are typically not repeated in the genome and the mRNA does not include recognizable repetitive sequence.

Animals↗