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D Schild

Publications and source records attributed to D Schild.

At least 55 records · Page 3Linked to original sources
PubMed1992

Identification of RAD16, a yeast excision repair gene homologous to the recombinational repair gene RAD54 and to the SNF2 gene involved in transcriptional activation.

The RAD54 gene of Saccharomyces cerevisiae is involved in the recombinational repair of DNA damage. The predicted amino acid sequence of the RAD54 protein shows significant homologies with the yeast SNF2 protein, which is required for the transcriptional activation of a number of diversely regulated genes. These proteins are 31% identical in a 492-amino acid region that includes presumed nucleotide and Mg2+ binding sites. We noted previously that the SNF2 protein also shares homology with a partial open reading frame (ORF) that was reported with the sequence of an adjacent gene. This ORF also shares homology with the RAD54 protein. To test whether this ORF is involved in transcriptional activation or DNA repair, yeast strains deleted for part of it have been isolated. These strains do not show a Snf-like phenotype, but they are UV sensitive. This gene has been identified as RAD16, a gene involved in the excision repair of DNA damage. Analysis of the rad16 deletion mutations indicates that RAD16 encodes a non-essential function and is not absolutely required for excision repair. Outside the region of homology to RAD54 and SNF2, the predicted RAD16 protein contains a novel cysteine-rich motif that may bind zinc and that has been found recently in eleven other proteins, including the yeast RAD18 protein. The homologies between RAD16, RAD54 and SNF2 are also shared by several additional, recently isolated yeast and Drosophila genes.

Adenosine Triphosphatases↗
PubMed1992

Significance of glomerular compartmentalization for olfactory coding.

This paper deals with the dendritic signal processing by mitral cells in the olfactory bulb and its meaning for olfactory coding. The output signals of olfactory receptor neurones are sent to the olfactory bulb where they converge onto the secondary neurones, the mitral cells. On a short time scale, the connectivity between receptor and mitral cells can be assumed to be constant, whereas on a longer time scale, when considering the ongoing de- and regeneration, it is necessary to model the synaptical weights between receptor and mitral cells as variables. In a first approach we used Hebb's rule to this end and presumed that a mitral cell can be represented by one compartment only. In this case, and with a sequence of realistically modeled receptor activity signals, the synaptical weights of all mitral cells converged to the same point though every mitral cell had initial weights different from those of any other mitral cell. This means that a mitral cell, when modeled as one compartment, does not become sensitive to any particular odor quality. A similar lack of quality tuning turned out to occur when one-compartment mitral cells were connected among each other by laterally inhibiting interneurones. We therefore took into account the glomerular fine structure of mitral cell dendrites, assuming electrotonically decoupled dendritic subbranches. This feature together with local inhibitory circuitry at the subbranches led to a fundamentally different type of synaptical convergence pattern. In this case, mitral cells developed differential sensitivities for different odors. Mitral cells have thus to be regarded as multicompartment cells, and local, non-Hebbian learning rules for their afferent synapses are necessary to achieve a reasonable map of odors upon mitral cell activities.

Animals↗
PubMed1991

Sequence of RAD54, a Saccharomyces cerevisiae gene involved in recombination and repair.

The complete nucleotide sequence of the RAD54 gene of the yeast Saccharomyces cerevisiae has been determined. The sequenced region contains an open reading frame of 2694 bp, and the predicted RAD54 protein has a potential nucleotide-binding site and possible nuclear targeting sequences. Northern analysis reveals a transcript of approx. 3.0 kb which is induced following x-ray irradiation.

Amino Acid Sequence↗
PubMed1991

Cloning and in vivo expression of the human GART gene using yeast artificial chromosomes.

Two Yeast Artificial Chromosomes (YACs) were isolated each with a full-length copy of the human gene that encodes the trifunctional protein containing phosphoribosylglycinamide synthetase (GARS), phosphoribosylglycinamide formyltransferase (GART) and phosphoribosylaminoimidazole synthetase (AIRS). The YACs were characterized by restriction mapping and by in situ hybridization of cosmid subclones containing the YAC ends to human metaphase chromosomes. One of the YACs contains co-cloned non-contiguous DNA whereas the other appears to have a single 600 kbp insert from 21q22.1, the location of the GART gene. A restriction map of the gene was obtained from two cosmid subclones which together span the 40 kb gene. The gene is functional when YAC DNA is transferred into GARS- or GARS-and-AIRS-deficient Chinese Hamster Ovary cells. The gene transfer was carried out both by lipofection using purified yeast DNA and by fusion between yeast spheroplasts and the hamster cells. Restriction analysis of DNA from cell lines whose purine auxotrophy was complemented by the YAC showed that with either method a complete and unrearranged copy of the gene can be transferred. The majority of the fusion cell lines appear to contain at least 80% of the YAC.

Acyltransferases↗
PubMed1991

Ca2+ modulates an unspecific cation conductance in olfactory cilia of Xenopus laevis.

Olfactory neurones of Xenopus laevis were studied by the patch clamp technique under voltage-clamp conditions. Isolated receptor cells were obtained by dissociating the olfactory mucosa in a Ca(2+)-free solution. Usually some of the resulting isolated olfactory cells lost all of their cilia during the dissociation procedure. Comparing the currents of cells with cilia to those of cells without cilia, a marked difference was found. When all known voltage-gated currents except the Ca(2+)-current were blocked, cells without cilia showed the voltage-gated Ca(2+)-current alone whereas cells with cilia clearly had an additional conductance gc. It could be activated in two ways, either by Ca2+ entry through Ca(2+)-channels or by Ca2+ entry through the Na/Ca-exchanger working in the reversed mode at positive membrane potentials. This ciliar conductance gc had its reversal potential at 0 mV. Replacing extracellular Cl- by isethionate on the one hand, and Na+ by Cs+ or N-methyl-D-glucamine on the other showed that gc was permeable for cations but not for Cl-. In conclusion, there appears to be a Ca(2+)-dependent unselective cation conductance on the cilia of olfactory neurones. The probable role of gc as the last step an IP3/Ca mediated transduction pathway is suggested.

Animals↗
PubMed1991

Expression of a human cDNA encoding a protein containing GAR synthetase, AIR synthetase, and GAR transformylase corrects the defects in mutant Chinese hamster ovary cells lacking these activities.

The isolation of a human cDNA encoding the multifunctional protein containing GAR synthetase, AIR synthetase, and GAR transformylase by functional complementation of purine auxotrophy in yeast has been reported. Chinese hamster ovary (CHO) cell mutant purine auxotrophs deficient in GAR synthetase (Ade-C) or AIR synthetase plus GAR transformylase (Ade-G) activities were transfected with this human GART cDNA subcloned into a mammalian expression vector. This restored 49-140% of the activities of GAR synthetase, AIR synthetase, and GAR transformylase in transfected cells when compared to wild-type CHO K1 parental cells. Study of one stably expressing transfectant, AdeC2, revealed that the human GART cDNA was incorporated into the CHO genome. The enzyme activities appear to be associated with an expressed protein of 110 kDa, very similar to that of purified human GART trifunctional enzyme. The Ade-C mutant shows reduced amounts of GART mRNA compared to CHO K1 and a protein of apparently reduced size, results consistent with the purine requirement and enzyme deficiency observed in the mutant. These experiments provide definitive evidence that the human GART cDNA encodes and can direct the production of active human GART trifunctional protein in mammalian cells. They also provide important evidence that the Ade-C and Ade-G mutants of CHO cells are defective in this gene.

Acyltransferases↗
PubMed1990

Cloning of three human multifunctional de novo purine biosynthetic genes by functional complementation of yeast mutations.

Functional complementation of mutations in the yeast Saccharomyces cerevisiae has been used to clone three multifunctional human genes involved in de novo purine biosynthesis. A HepG2 cDNA library constructed in a yeast expression vector was used to transform yeast strains with mutations in adenine biosynthetic genes. Clones were isolated that complement mutations in the yeast ADE2, ADE3, and ADE8 genes. The cDNA that complemented the ade8 (phosphoribosylglycinamide formyltransferase, GART) mutation, also complemented the ade5 (phosphoribosylglycinamide synthetase) and ade7 [phosphoribosylaminoimidazole synthetase (AIRS; also known as PAIS)] mutations, indicating that it is the human trifunctional GART gene. Supporting data include homology between the AIRS and GART domains of this gene and the published sequence of these domains from other organisms, and localization of the cloned gene to human chromosome 21, where the GART gene has been shown to map. The cDNA that complemented ade2 (phosphoribosylaminoimidazole carboxylase) also complemented ade1 (phosphoribosylaminoimidazole succinocarboxamide synthetase), supporting earlier data suggesting that in some organisms these functions are part of a bifunctional protein. The cDNA that complemented ade3 (formyltetrahydrofolate synthetase) is different from the recently isolated human cDNA encoding this enzyme and instead appears to encode a related mitochondrial enzyme.

Acyltransferases↗
PubMed1989

Whole-cell currents in olfactory receptor cells of Xenopus laevis.

Olfactory mucosae of Xenopus laevis were dissociated without enzymatic treatment and the isolated olfactory neurones were studied with the tight-seal whole-cell recording configuration of the patch clamp technique. In the voltage clamp, five current components could be distinguished: a fast, TTX-sensitive Na+-current, a small and slow inward current carried by Ca2+ ions, a Ca2+-dependent K+-current, a K+-current which activates rapidly at voltages more positive than -20 mV and quickly inactivates, and a slowly activating and very slowly inactivating K+-current. Some of the characteristics of the whole-cell currents herein reported contradict previous findings while others verify them, thereby allowing a tentative interpretation of their physiological role in the transduction process.

Animals↗
PubMed1989

Two DNA repair and recombination genes in Saccharomyces cerevisiae, RAD52 and RAD54, are induced during meiosis.

The DNA repair and recombination genes of Saccharomyces cerevisiae, RAD52 and RAD54, were transcriptionally induced approximately 10- to 15-fold in sporulating MATa/alpha cells. Congenic MATa/a cells, which did not sporulate, did not show similar increases. Assays of beta-galactosidase activity in strains harboring either a RAD52- or RAD54-lacZ gene fusion indicated that this induction occurred at a time concomitant with a commitment to meiotic recombination, as measured by prototroph formation from his1 heteroalleles.

DNA Repair↗
PubMed1988

Principles of odor coding and a neural network for odor discrimination.

A concept of olfactory coding is proposed. It describes the stimulus responses of all receptor cells by the use of vector spaces. The morphological convergence pattern between receptor cells and glomeruli is given in the same vector space as the receptor cell activities. The overall input of a glomerulus follows as the scalar product of the receptor cell activity vector and the vector of the glomerulus' convergence pattern. The proposed coding concept shows how the network of the olfactory bulb succeeds in discriminating odors with high selectivity. It is concluded that sets of mitral cells coding similar odors work very much in the way of mutually inhibited matched filters. This solves one main problem both in olfaction as well as real-time odor detection by an artificial nose, i.e., how the fairly low degree of selectivity of receptor cells or sensors is overcome by the neural network following the receptor stage. The formal description of olfactory coding suggests that quality perception which is invariant under concentration shifts is accomplished by an associative memory in the olfactory bulb.

Animals↗
PubMed1987

Response pattern features of mitral cells in the goldfish olfactory bulb.

Temporal discharge characteristics of goldfish olfactory bulb mitral cells are investigated. In contrast to earlier findings, it has been shown that every response is determined by only two features, namely, the mean activities of the early and the late response (dynamic and static response component). As both activities can be lower than, indistinguishable from, or higher than prestimulus activity, the two response features correspond to 9 possible response pattern types.

Action Potentials↗
PubMed1987

Regulation of RAD54- and RAD52-lacZ gene fusions in Saccharomyces cerevisiae in response to DNA damage.

The RAD52 and RAD54 genes in the yeast Saccharomyces cerevisiae are involved in both DNA repair and DNA recombination. RAD54 has recently been shown to be inducible by X-rays, while RAD52 is not. To further investigate the regulation of these genes, we constructed gene fusions using 5' regions upstream of the RAD52 and RAD54 genes and a 3'-terminal fragment of the Escherichia coli beta-galactosidase gene. Yeast transformants with either an integrated or an autonomously replicating plasmid containing these fusions expressed beta-galactosidase activity constitutively. In addition, the RAD54 gene fusion was inducible in both haploid and diploid cells in response to the DNA-damaging agents X-rays, UV light, and methyl methanesulfonate, but not in response to heat shock. The RAD52-lacZ gene fusion showed little or no induction in response to X-ray or UV radiation nor methyl methanesulfonate. Typical induction levels for RAD54 in cells exposed to such agents were from 3- to 12-fold, in good agreement with previous mRNA analyses. When MATa cells were arrested in G1 with alpha-factor, RAD54 was still inducible after DNA damage, indicating that the observed induction is independent of the cell cycle. Using a yeast vector containing the EcoRI structural gene fused to the GAL1 promoter, we showed that double-strand breaks alone are sufficient in vivo for induction of RAD54.

Cell Cycle↗
PubMed1985

A mapping method for Saccharomyces cerevisiae using rad52-induced chromosome loss.

Saccharomyces cerevisiae diploids homozygous for the rad52-1 mutation have previously been shown to lose chromosomes mitotically. Spontaneous events and events following low levels of X-ray or methyl methanesulfonate treatment result in monosomic diploids, whereas higher levels of treatment result in near haploidization. This rad52-1-dependent chromosome loss has been used to develop a new mapping method which can be used to assign a previously unmapped gene to a chromosome. Chromosome loss mapping can be done in either of two ways: if a diploid, homozygous for rad52-1 but heterozygous for a variety of other recessive markers, is constructed with an unmapped recessive mutation in coupling with known chromosomal markers, chromosome loss will result in the coordinate expression of the mutation and other recessive markers on the same chromosome; if, however, the diploid is constructed with the unmapped mutation in repulsion to chromosomal markers, then even haploidization will never result in the coordinate expression of the unmapped mutation and other markers on the same homologous chromosome pair--This mapping method and subsequent tetrad analyses have been used to locate hom6 on chromosome X, ade4 on chromosome XIII and cdc31 on chromosome XV and to demonstrate that met5, previously assigned to chromosome V, actually maps to chromosome X; the met- marker on chromosome V has been shown to be met6. GAL80 and SUP5, previously assigned to an unmapped fragment, have now been mapped to the right arm of chromosome XIII.

Chromosome Deletion↗
PubMed1985

Temporal changes in mitral cell response patterns during repeated odor exposure.

The olfactory system of 17 goldfish was stimulated by natural odors, and from 31 mitral cells activity was extracellularly recorded as a response to the stimuli. 40 experiments were available for evaluation because nine of the 31 cells were investigated with respect to two different odors. The aim of this study was to examine the changes of the activity patterns during repeated runs of an experiment. 120 runs were taken in 15 experiments, 40 runs in 25 experiments, and 37 runs in 2 experiments. Nineteen out of the forty recordings showed patterned activities. In ten cases the patterns remained constant in all runs, while pattern changes occurred in nine cases. These changes sometimes happened abruptly after the first run or developed gradually over up to forty runs in other cases. Possible causes of the pattern changes are discussed.

Animals↗