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J Piskur

Publications and source records attributed to J Piskur.

48 records · Page 3Linked to original sources
PubMed1994

A mechanochemical study of MgDNA fibers in ethanol-water solutions.

Highly oriented calf-thymus MgDNA fibers, prepared by a wet spinning method, were studied with a simple mechanochemical set-up. The relative fiber length, L/Lo, was measured with the fibers submerged in ethanol-water solutions. In one type of experiment L/Lo was measured as a function of ethanol concentration at room temperature. No substantial decrease in L/Lo with increasing ethanol concentration was observed, indicating that MgDNA fibers stay in the B form even when the water activity is very low. For low ethanol concentrations the fiber structure is stable and does not dissolve even at very high water activities. In a second type of experiment, the heat-induced helix-coil transition was manifested by a marked contraction of the fibers. The transition temperature decreases linearly with increasing ethanol concentration between 52 and 68% ethanol. At higher ethanol concentrations the helix-coil transition temperature increases due to strong aggregation within the DNA fibers, and above 77% ethanol the fibers do not contract at all, not even at the upper temperature limit of the experiments, approximately 80 degrees C. This behavior is discussed with reference to dried DNA and the P form of DNA. The helix-coil transition temperature of the MgDNA fibers in 70% ethanol does not show any dependence on the MgCl2 concentration. It is shown that the Poisson-Boltzmann cylindrical cell model can account qualitatively for this lack of salt dependence.

Animals↗
PubMed1993

The dominant mutation Suppressor of black indicates that de novo pyrimidine biosynthesis is involved in the Drosophila tan pigmentation pathway.

A deficiency in the production of beta-alanine causes the black (b) phenotype of Drosophila melanogaster. This phenotype is normalized by a semi-dominant mutant gene Su(b) shown previously to be located adjacent to or within the rudimentary (r) locus. The r gene codes for three enzyme activities involved in de novo pyrimidine biosynthesis. Pyrimidines are known to give rise to beta-alanine. However, until recently it has been unclear whether de novo pyrimidine biosynthesis is directly coupled to beta-alanine synthesis during the tanning process. In this report we show that flies carrying Su(b) can exhibit an additional phenotype, resistance to toxic pyrimidine analogs (5-fluorouracil, 6-azathymine and 6-azauracil). Our interpretation of this observation is that the pyrimidine pool is elevated in the mutant flies. However, enzyme assays indicate that r enzyme activities are not increased in Su(b) flies. Genetic mapping of the Su(b) gene now places the mutation within the r gene, possibly in the carbamyl phosphate synthetase (CPSase) domain. The kinetics of CPSase activity in crude extracts has been studied in the presence of uridine triphosphate (UTP). While CPSase from wild-type flies was strongly inhibited by the end-product, UTP, CPSase from Su(b) was inhibited to a lesser extent. We propose that diminished end-product inhibition of de novo pyrimidine biosynthesis in Su(b) flies increases available pyrimidine and consequently the beta-alanine pool. Normalization of the black phenotype results.

Animals↗
PubMed1993

Folding and secretion of Saccharomyces cerevisiae carboxypeptidase Y are influenced by fusion with short heterologous peptides.

High levels of secreted yeast carboxypeptidase Y can be obtained in yeast by regulated overexpression under the control of the GAL1 promoter. Carboxypeptidase Y was investigated as a potential carrier for expression of heterologous oligopeptides. Coding sequences for two pentapeptides, Hepp (H-Asp-Ser-Asp-Pro-Arg-OH) and a thymopentin analogue (H-Arg-Pro-Asp-Val-Tyr-OH), and an analogue of salmon calcitonin, were inserted into, or added on to, the coding sequence for carboxypeptidase Y, and the plasmids were introduced into a yeast mutant that mis-sorts vacuolar proteins. Translation efficiency of mRNA from the expression plasmids encoding hybrid carboxypeptidase Y was apparently not influenced by the insert. However, secretion of the hybrid proteins was lower than that of wild-type carboxypeptidase Y. A major fraction of the hybrid proteins accumulated intracellularly as a form characteristic for the endoplasmic reticulum. The results suggest that the inserted peptides influenced the secretion through the position and sequence effect on post-translational events. Furthermore, studies on folding properties indicated that the in vitro refolding capacity of the hybrid proteins was reduced. Thus, in the case of insertions, the transition from an unfolded chain to the correctly folded protein was likely to be disfavoured by misfolding. However, the tendency towards misfolding could be partially suppressed by changing the insertion site, and secretion was most effective in the cases of C-terminal fusions.

Amino Acid Sequence↗
PubMed1992

Effect of reading a summary of research about biological bases of homosexual orientation on attitudes toward homosexuals.

The effect of exposure to information regarding the development of homosexual orientation on attitudes toward homosexuals was investigated. Testing was conducted in five regularly scheduled undergraduate classes. 105 volunteer subjects from college classes were exposed to one of three treatment conditions. Subjects in the experimental group read a summary article of current research emphasizing a biological component of homosexual orientation. Subjects in one control group read a summary article of research focusing on the absence of hormonal differences between homosexual and heterosexual men. Subjects in another control group were not exposed to either article. All subjects completed the Index of Attitudes Toward Homosexuals. As predicted, subjects in the experimental group had significantly lower scores than subjects in the control groups. There was a significant interaction between treatment condition and sex of subject. Scores on the index were significantly lower for women, but only in the experimental group. These results show that exposure to a research summary can significantly affect immediately assessed scores on the Index of Attitudes Toward Homosexuals. Also, the pattern of effects of these experiences was different for women and men.

Adolescent↗
PubMed1989

Respiratory-competent yeast mitochondrial DNAs generated by deleting intergenic regions.

Two respiratory-competent yeast strains having mitochondrial (mt) DNA characterized by single non-overlapping deletions, encompassing intergenic sequences, have been crossed. Diploid daughter clones have been screened by electrophoresis of mtDNA fragments, and a respiratory-competent clone (ER8.75), having a recombinant small mtDNA with both parental deletions, has been detected. ER8.75 mtDNA lacks around 20% of wild-type intergenic sequences, encompassing three ori/rep sequences. This mutant could be helpful in analyzing the organelle genome and, particularly, the function of intergenic sequences.

Chromosome Deletion↗
PubMed1989

Transmission of the yeast mitochondrial genome to progeny: the impact of intergenic sequences.

In a previous publication it was shown that the output of yeast mitochondrial loci lacking nearby intergenic sequences (encompassing ori/rep elements) was reduced in crosses to strains with wild-type mtDNAs. In the present work, mitochondrial genomes carrying the intergenic deletions were marked at unlinked loci by introducing specific antibiotic resistance mutations against erythromycin, oligomycin and paromomycin. These marked genomes were used to follow the output of unlinked regions of the genome from crosses between the intergenic deletion mutants and wild-type strains. Transmission of genetically unlinked markers in coding regions was substantially reduced when an intergenic deletion was present on the same genome. In general the transmission of the antibiotic markers was the same as or slightly higher than the corresponding intergenic marker. These results indicate that the presence of an intergenic deletion in the regions studied impairs the transmission to progeny of a mitochondrial genome as a whole. More specifically, the results suggest that ori/rep sequences, present in the regions that have been deleted, confer a competitive advantage over genomes lacking a full complement of such sequences. These results support the hypothesis that intergenic sequences, and specifically ori/rep elements, have a biological role in the mitochondrial genome. However, because of the exclusive presence of ori/rep sequences in the genus Saccharomyces, it may be that these sequences evolved in (or invaded) the mitochondrial genome relatively late in the evolution of the yeasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1988

Sensitivity of intergenic regions of yeast mitochondrial DNA to single-strand-specific nucleases.

The reactivity of mitochondrial DNA (mtDNA) sequences from Torulopsis glabrata and Saccharomyces cerevisiae towards single-strand-specific nucleases has been examined. AT-rich stretches located in intergenic sequences from both yeasts were cleaved by nucleases when the sequences were contained in supercoiled plasmid DNA. In particular ori/rep sequences from the mtDNA of S. cerevisiae were shown to be sensitive to the single-strand-specific nucleases. The locations of the sensitive sites were related to the organisation of the sequence domains of ori/rep and the superhelicity of the DNA, as well as the presence of particular sequences. It is proposed that distortions of the DNA duplex could be generated in mtDNA molecules in vivo and that these distortions may provide a substrate for enzymes involved in transmission, recombination and/or transcription of mtDNA.

Candida↗
PubMed1988

A 5 kb intergenic region containing ori1 in the mitochondrial DNA of Saccharomyces cerevisiae is dispensable for expression of the respiratory phenotype.

A mutant mitochondrial DNA of Saccharomyces cerevisiae strain R 0.54 has been shown to have a 5 kb deletion which removes the ori1 sequence and its surrounding intergenic sequences between the pro tRNA and 15 S rRNA genes. The deleted DNA has been sequenced and is found to be flanked by two 11 bp direct repeats. The deletion mutant displays a normal phenotype in non-fermentable media. This implies that the intergenic sequence is not required for expression of the respiratory phenotype.

Base Sequence↗
PubMed1988

Transmission of yeast mitochondrial loci to progeny is reduced when nearby intergenic regions containing ori sequences are deleted.

Mitochondrial DNAs (mtDNA) from four stable revertant strains generated from high frequency petite forming strains of Saccharomyces cerevisiae have been shown to contain deletions which have eliminated intergenic sequences encompassing ori1, ori2 and ori7. The deleted sequences are dispensable for expression of the respiratory phenotype and mutant strains exhibit the same relative amount of mtDNA per cell as the wild-type (wt) parental strain. These deletion mutants were also used to study the influence of particular intergenic sequences on the transmission of closely linked mitochondrial loci. When the mutant strains were crossed with the parental wt strains, there was a strong bias towards the transmission into the progeny of mitochondrial genomes lacking the intergenic deletions. The deficiency in the transmission of the mutant regions was not a simple function of deletion length and varied between different loci. In crosses between mutant strains which had non-overlapping deletions, wt mtDNA molecules were formed by recombination. The wt recombinants were present at high frequencies among the progeny of such crosses, but recombinants containing both deletions were not detected at all. The results indicate that mitochondrial genomes can be selectively transmitted to progeny and that two particular intergenic regions positively influence transmission. Within these regions other sequences in addition to ori/rep affect transmission.

Base Sequence↗