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R J Britten

Publications and source records attributed to R J Britten.

At least 109 records · Page 6Linked to original sources
PubMed1983

Mitochondrial DNA sequences in the nuclear genome of Strongylocentrotus purpuratus.

Two sea urchin embryo complementary DNA clones representing mitochondrial 16 S ribosomal RNA and cytochrome oxidase subunit I messenger RNA have been characterized. The cloned cDNAs are colinear with sea urchin mitochondrial DNA, and their identification is based on cross-hybridization with known restriction fragments of human mitochondrial DNA, and on nucleotide sequence determinations. The mitochondrial cDNA clones also displayed an unexpected reaction with specific genomic DNA sequences in gel blot hybridizations. Genomic phage lambda recombinants containing sequences hybridizing with the mitochondrial clones were isolated and the arrangement of these sequences was determined. The genomic region studied contains a sequence homologous with the 3' end of the mitochondrial 16 S rRNA gene, flanked on one side by what is possibly a complete copy of the cytochrome oxidase subunit I gene, and on the other by a duplication of a fragment of this gene. The nucleotide sequence divergence between the mitochondrial and nuclear homologues of the cytochrome oxidase subunit I gene varies for different regions of the gene, from about 13% to 25%, while there is about 8% sequence divergence between nuclear and mitochondrial versions of the 3' 16S rRNA sequence. The structure of the genomic mitochondrial sequence homologues indicates that during sea urchin evolution there occurred a germ-line transposition of a fragment of the mitochondrial genome into the nuclear DNA, followed by rearrangements and single nucleotide substitutions.

Animals↗
PubMed1983

Poly(A) RNA of the egg cytoplasm: structural resemblance to the nuclear RNA of somatic cells.

This paper concerns the structural characteristics of the poly(A) RNA stored in unfertilized amphibian and echinoderm eggs. Though located in the egg cytoplasm, at least two-thirds of these maternal transcripts display an interspersed sequence organization similar to that of nuclear RNA. In Xenopus laevis interspersed poly(A) RNA molecules are synthesized and deposited in the oocyte cytoplasm throughout the main growth phase of oogenesis. Regions of the sea urchin genome that are represented by interspersed maternal transcripts have been recovered from recombinant clone libraries. In one case the same single-copy sequence is found both in an abundant message-sized 1.6 kilobase (kb) maternal transcript and in a 7.5 kb maternal transcript that structurally resembles a precursor form and is not found in embryonic polysomes. In a second example considered, a 9.5 kb transcript was identified in embryo nuclear RNA that may be identical in structure with an interspersed maternal poly(A) RNA derived from the same transcription unit. Transcription of this sequence appears to be constitutive in somatic cell nuclei, though no homologous cytoplasmic RNAs are found after early cleavage. This may be a widespread form of regulation for transcription units expressed in female germ cells, and represented in the maternal poly(A) RNA pools of unfertilized eggs.

Animals↗
PubMed1983

Transcripts of three mitochondrial genes in the RNA of sea urchin eggs and embryos.

cDNA clones representing mitochondrial 16 S rRNA, and mRNAs for cytochrome oxidase I and an unidentified reading frame were used to measure the prevalence and stability of these transcripts in gastrula stage embryos. The 16 S rRNA is the most prevalent embryo poly(A) RNA, and is synthesized about four times more rapidly than is the mRNA for cytochrome oxidase. The relative prevalence of the two mRNAs is largely determined by their turnover rates.

Animals↗
PubMed1983

Comparison of sea urchin and human mtDNA: evolutionary rearrangement.

Clones of full-length mtDNA have been isolated from a Strongylocentrotus franciscanus recombinant DNA library by screening a cDNA clone of cytochrome oxidase subunit 1 mRNA. Restriction fragment cross-hybridization analysis shows the following difference in gene arrangement between sea urchin and human mtDNA. The 16S rRNA and cytochrome oxidase subunit 1 genes are directly adjacent in sea urchin mtDNA. These two genes are separated in human and other mammalian mtDNAs by the region containing unidentified reading frames 1 and 2. In spite of the difference in gene order, gene polarity appears to have been conserved. We conclude that the difference in gene order reflects a rearrangement that took place in the sea urchin lineage since sea urchins and mammals last shared a common ancestor.

Animals↗
PubMed1982

Molecular biology of the sea urchin embryo.

Research on the early development of the sea urchin offers new insights into the process of embryogenesis. Maternal messenger RNA stored in the unfertilized egg supports most of the protein synthesis in the early embryo, but the structure of maternal transcripts suggests that additional functions are also possible. The overall developmental patterns of transcription and protein synthesis are known, and current measurements describe the expression of specific genes, including the histone genes, the ribosomal genes, and the actin genes. Possible mechanisms of developmental commitment are explored for regions of the early embryo that give rise to specified cell lineages, such as the micromere-mesenchyme cell lineage.

Actins↗
PubMed1981

Molecular structure of maternal RNA.

The presence of a stable maternal mRNA population in mature oocytes of many species is well established. In this paper we show that the mature egg contains, in addition to these mature mRNAs, a structurally more complex population of RNA transcripts. This latter class of RNA consists of polyadenylated transcripts of repetitive and nonrepetitive DNA elements covalently linked into long interspersed molecules. As much as seventy percent of the polyadenylated egg RNA of Xenopus laevis and Strongylocentrotus purpuratus is represented in this interspersed population. Most of the nonrepetitive DNA sequences represented in the mature mRNA population are also present in the interspersed RNA. These transcripts have an organization similar to that of somatic cell nuclear RNA. Data are presented that suggests some of these interspersed maternal transcripts are unprocessed precursor-like molecules. Some possible functions of this novel class of RNA during early development are discussed.

Animals↗
PubMed1981

Long and short repeats of sea urchin DNA and their evolution.

Repeated sequences cloned from the DNA of the sea urchin S. purpuratus were used as probes to measure the lengths of individual families of repeats. Some probes reassociated much more rapidly with preparations of long repeats than with short repeats while others reassociated more rapidly with short repeats than with long repeats. In this way two of five cloned repeats were shown to represent families with a great majority of sequences in the long class. One represented a family with similar number of long and short class members. Two were members of predominantly short class families - The cloned repeats representing long class families, formed more precise duplexes than those representing short class families. Thermal stability measurements using S. purpuratus or S. franciscanus driver DNA showed that precise repetitive sequences have as great an interspecies sequence difference as the less precise repeats. Thus the precision of many families may result from recent multiplication rather than from selective pressure on the DNA sequences. Measurements of evolutionary frequency change show a clear correlation between the frequency change and the size of families of repeats in S. purpuratus. Comparison with S. franciscanus indicates that many of the large size families in S. purpuratus are those that have grown in size since these two species diverged.

Animals↗
PubMed1981

Evolutionary distances in Hawaiian Drosophila measured by DNA reassociation.

Comparisons of the sequence divergence of three species of Hawaiian Drosophila have been made by hybridization of single-copy tracer DNA of each of the species with driver DNA from each species, and measurement of the average melting temperature (Tma) in a chaotropic solvent (2.4 M tetraethylammonium chloride) which minimizes differences due to base composition. Correction was made for the length of hybrid duplex regions to obtain the reduction in thermal stability due to divergence. An accuracy of +/- 0.2 degrees C was achieved and the mean reduction in Tm for hybridization between D. heteroneura and D. silvestris (found only on the island of Hawaii) was 0.55 degrees C and between D. picticornis, found only on the island of Kauai, and the other two species was 2.13 degrees C. The rate of DNA change is estimated to be between 0.2 and 0.4%/My by assuming that the D. heteroneura-D. silvestris divergence occurred 0.8 My ago and the divergence between these species and D. picticornis between 4 and 6 My ago. The general single copy DNA sequence divergence appears to be very much greater than the minimal coding region sequence divergence previously estimated from allozyme studies.

Animals↗
PubMed1981

Organization and expression of multiple actin genes in the sea urchin.

A set of at least 11 actin genes has been isolated from genomic recombinant deoxyribonucleic acid libraries of the sea urchin Strongylocentrotus purpuratus. Most of the isolates derive from a library which represents the genome of a single animal. There are at least five distinct types of sea urchin actin gene, some of which are represented by multiple copies in the genome. The actin gene types are distinguished by nonhomologous flanking sequences and intervening sequences, though the protein coding sequences appear in most cases to be quite similar. Eight of the 11 genes isolated have been recovered in lambda recombinants that contain two actin genes, linked at 5- to 9-kilobase distances. Restriction map overlaps suggest that the genome contains an array of at least three of these genes spaced over about 30 kilobases of deoxyribonucleic acid. In the linkage patterns observed, actin genes of diverse types were linked to each other. In early embryos, actin messenger ribonucleic acid (RNA) transcripts of 1.8 and 2.2 kilobases were found, and the longer of these transcripts was more prevalent in the maternal RNA of the egg. From RNA gel blot experiments, we conclude that the two transcripts derive from different actin gene types. Different repetitive sequences were located to either side of most of the actin genes, and in most observed cases the repeat sequences which were adjacent to actin genes of a given type were similar. The repeat sequences flanking the actin genes belonged to families which were transcribed, but those repeats in the neighborhood of the actin genes which have been investigated were not themselves represented in the stable RNAs of eggs or early embryos.

Actins↗