Search PubMed⌕ Search

Biomedical subjects

D B Stern

Publications and source records attributed to D B Stern.

66 records · Page 4Linked to original sources
PubMed1986

The watermelon mitochondrial URF-1 gene: evidence for a complex structure.

We have cloned and sequenced a fragment of watermelon mitochondrial DNA (mtDNA) which contains a gene homologous to mitochondrial URF-1 (Unidentified Reading Frame-1) of vertebrates, Drosophila yakuba and Aspergillus nidulans. URF-1 is thought to encode a component of the respiratory chain NADH dehydrogenase. Two coding regions in the watermelon gene are separated by approximately 1,450 bp of untranslatable DNA. These two exons encode the central portions of URF-1, and are highly conserved. We postulate that three additional exons, selected by their map location and amino acid homology to other URF-1 sequences, encode the remainder of the polypeptide. This is the first description of a plant mitochondrial gene with multiple introns.

Amino Acid Sequence↗
PubMed1985

Mitochondrial gene expression in Cucurbitaceae: conserved and variable features.

We have examined mitochondrial DNA (mtDNA) sequence conservation, transcriptional patterns of mitochondrial genes, and mitochondrial translation products in four species of the plant family Cucurbitaceae, in which there is a seven-fold range in mitochondrial genome size. A set of conserved mtDNA sequences which we term "core" DNA is present in all cucurbit genomes examined. In watermelon, only those mtDNA restriction fragments which contain "core" DNA hybridize with mtRNA. Similar numbers of polypeptides are synthesized by isolated mitochondria from all species examined, but an extra set of mtDNA sequences is transcribed in the largest genome (muskmelon). Taken together, these results suggest that some mtRNA is untranslated in muskmelon. Cloned mitochondrial genes of known function, from maize, identified mitochondrial transcripts that varied in both size and number among cucurbit species.

Base Sequence↗
PubMed1984

Recombination sequences in plant mitochondrial genomes: diversity and homologies to known mitochondrial genes.

Several plant mitochondrial genomes contain repeated sequences that are postulated to be sites of homologous intragenomic recombination (1-3). In this report, we have used filter hybridizations to investigate sequence relationships between the cloned mitochondrial DNA (mtDNA) recombination repeats from turnip, spinach and maize and total mtDNA isolated from thirteen species of angiosperms. We find that strong sequence homologies exist between the spinach and turnip recombination repeats and essentially all other mitochondrial genomes tested, whereas a major maize recombination repeat does not hybridize to any other mtDNA. The sequences homologous to the turnip repeat do not appear to function in recombination in any other genome, whereas the spinach repeat hybridizes to reiterated sequences within the mitochondrial genomes of wheat and two species of pokeweed that do appear to be sites of recombination. Thus, although intragenomic recombination is a widespread phenomenon in plant mitochondria, it appears that different sequences either serve as substrates for this function in different species, or else surround a relatively short common recombination site which does not cross-hybridize under our experimental conditions. Identified gene sequences from maize mtDNA were used in heterologous hybridizations to show that the repeated sequences implicated in recombination in turnip and spinach/pokeweed/wheat mitochondria include, or are closely linked to genes for subunit II of cytochrome c oxidase and 26S rRNA, respectively. Together with previous studies indicating that the 18S rRNA gene in wheat mtDNA is contained within a recombination repeat (3), these results imply an unexpectedly frequent association between recombination repeats and plant mitochondrial genes.

Base Sequence↗
PubMed1984

Extensive and widespread homologies between mitochondrial DNA and chloroplast DNA in plants.

We used hybridization techniques to demonstrate that numerous sequence homologies exist between cloned mung bean and spinach chloroplast DNA (ctDNA) restriction fragments and mtDNAs from corn, mung bean, spinach, and pea. The strongest cross-homologies are between clones derived from the ctDNA inverted repeat and mtDNA from corn and pea, although all the ctDNA clones tested hybridized to at least one mtDNA restriction fragment. Known chloroplast genes showing strong mtDNA homologies include those for the large subunit of ribulosebisphosphate carboxylase, which hybridizes to corn mtDNA, and the beta subunit of the chloroplast ATPase, which hybridizes to mung bean mtDNA. Certain of these homologies were confirmed by using cloned spinach mtDNA restriction fragments as probes in reciprocal hybridizations to ctDNA. Several of these ctDNA-homologous mtDNA sequences were shown to be much more closely related to ctDNA from the same species than to that of a distantly related species. We interpret these differential homologies as evidence for relatively recent DNA sequence transfer events, suggesting that transpostion between the two genomes is an ongoing evolutionary process.

Journal Article↗
PubMed1983

Maize mitochondrial DNA contains a sequence homologous to the ribulose-1,5-bisphosphate carboxylase large subunit gene of chloroplast DNA.

The mitochondrial genome of maize contains a DNA sequence homologous to the chloroplast gene coding for the large subunit of ribulose-1,5-bisphosphate carboxylase (LS gene). The presence in mitochondrial DNA of both coding and flanking sequences of this gene has been demonstrated first, by cross hybridization between the purified organelle DNAs and between cloned mitochondrial and chloroplast DNA sequences and second, by in vitro transcription-translation of cloned mitochondrial DNA in an E. coli cell free system where a 21,000 dalton polypeptide is synthesized that can be precipitated with antibodies to wheat ribulose-1,5-bisphosphate carboxylase. In contrast to the 12 kb chloroplast homologous sequence found in the mitochondrial genome (Stern and Lonsdale, 1982), the sequence homologous to the LS gene is unaltered in mitochondrial DNA isolated from the male sterile cytoplasms of maize. The LS gene homologous sequence in the mitochondrial genome is located some 65 kb from the 18S mitochondrial rRNA gene and approximately 20 kb from the mitochondrial DNA sequence having homology to the chloroplast 16S rRNA gene.

Base Sequence↗
PubMed1982

Mitochondrial and chloroplast genomes of maize have a 12-kilobase DNA sequence in common.

A 12-kilobase DNA sequence has been identified in the maize mitochondrial genome which is homologous to part of the inverted repeat of the maize chloroplast genome. In chloroplasts the sequence contains a 16S rRNA gene, and also the coding sequences for tRNAIle and tRNAVal. Mitochondrial DNA from the male-sterile cytoplasms of maize is altered in this region.

Base Sequence↗
PubMed1982

Organization of the mitochondrial ribosomal RNA genes of maize.

The organisation of the mitochondrial ribosomal RNA genes in maize is described. Each of the rRNAs is encoded by a single gene. The 5S and 18S rRNA genes are close together, and separated from the 26S rRNA gene by 16 kb of DNA. There is no evidence of heterogeneity in this gene arrangement.

DNA Restriction Enzymes↗
PubMed1977

Handedness and the lateral distribution of conversion reactions.

The purpose of this investigation was to determine whether the observation of Ferenczi and Purves-Stewart that conversion reactions occur with higher frequency on the left side of the body than on the right side could be confirmed. Both right-handed and left-handed patients experienced a higher proportion of left-sided symptoms (weakness or paralysis; sensory loss or numbness) than would be expected by chance, indicating a lack of support for the hypothesis that unilateral conversion symptoms occur most frequently on the most "convenient" (nondominant) side of the body. These findings and prior reports of left-sided lateralization of psychogenic pain were interpreted as support for the hypothesis that the right cerebral hemisphere is particularly involved in the mediation of affectively or motivationally determined somatic symptoms. The question of a possible link between these results and certain symptoms of disease of the right hemisphere was raised.

Conversion Disorder↗
PubMedDate not supplied

Processing and degradation of chloroplast mRNA.

The conversion of genetic information stored in DNA into a protein product proceeds through the obligatory intermediate of messenger RNA. The steady-state level of an mRNA is determined by its relative synthesis and degradation rates, i.e., an interplay between transcriptional regulation and control of RNA stability. When the biological status of an organism requires that a gene product's abundance varies as a function of developmental stage, environmental factors or intracellular signals, increased or decreased RNA stability can be the determining factor. RNA stability and processing have long been known as important regulatory points in chloroplast gene expression. Here we summarize current knowledge and prospects relevant to these processes, emphasizing biochemical data. The extensive literature on nuclear mutations affecting chloroplast RNA metabolism is reviewed in another article in this volume (Barkan and Goldschmidt-Clermont, this issue).

Chloroplasts↗