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H M Seyfert

Publications and source records attributed to H M Seyfert.

36 records · Page 2Linked to original sources
PubMed1991

Genomic organization of the bovine alpha-S1 casein gene.

We report the sequence of the complete bovine alpha-s1 casein gene eludicating for the first time the genomic organization of an alpha-s type casein gene. Extending over 17508 bp the gene is split into 19 exons, ranging in size from 24 bp to 385 bp. Except for the translational stop codon not a single coding triplet of the alpha-s1 reading frame is disrupted by any of the splice junctions, which all confirm to known splice consensus sequences. Nine out of 16 coding exons begin with a 'GAX' codon, specific for glutamate. Splicing of this codon from exon 10 to the preceding exon creates a major phosphorylation site. An intron-exon-intron stretch of 154 bp comprising exons 10 and 13 is found precisely duplicated. Associated with the gene, copies of 8 atriodactyla retroposons are found, 6 of which are interspersed into the sequences of the three longest introns. We discuss the possibility that three functional parts of the gene have been recruited and evolutionary conserved at a time before gene diversification gave rise to the separate evolution of alpha- and beta-type casein-genes.

Animals↗
PubMed1989

Detection and interspecies-transformation of a beta-lactamase-encoding plasmid from Pasteurella haemolytica.

Pasteurella haemolytica-cultures, isolated from cattle with respiratory diseases, were investigated for their biotype, serotype, antimicrobial resistance and plasmid content. A plasmid encoding a beta-lactamase could be demonstrated in 9 of 19 Pasteurella haemolytica-cultures. These 9 cultures, all belonging to biotype A and serotype 1, were resistant to ampicillin, carbenicillin, penicillin G and ticarcillin. The plasmid of the respective cultures proved to be identical upon Southern blot hybridization. It could be transformed into Escherichia coli 490 A where it expressed again a beta-lactamase-activity.

Ampicillin Resistance↗
PubMed1987

Induced tubulin synthesis is caused by induced gene transcription in Tetrahymena.

Tubulin synthesis and tubulin m RNA concentrations increase to variable extents during ciliary regeneration in the ciliate Tetrahymena. Experiments described here were carried out to determine whether the increased tubulin mRNA concentrations are due to induced transcription of tubulin genes or to stabilization of tubulin mRNA. In vivo labeling experiments with [3H]uridine and in vitro transcription assays suggest that under conditions of increased protein and tubulin synthesis the rate of transcription is enhanced. Hybridization assays of in vitro transcribed RNA also demonstrate qualitatively that the tubulin genes are transcribed at higher rates when tubulin synthesis is stimulated during ciliary regeneration. This observation is supported by measurements of the half-life of tubulin mRNA molecules in nondeciliated cells: This is approximately 2 h. Since the concentration of tubulin mRNA in cells engaged in cilia regeneration increases from 5 to 19-fold during the first hour of the regeneration period, even a complete stabilization of the tubulin mRNA molecules could not account for an increase in tubulin mRNA concentration of this magnitude.

Animals↗
PubMed1987

The abundance of alpha-tubulin mRNA increases during ciliary regeneration in Tetrahymena, and this occurs independently of the soluble tubulin content.

Control mechanisms of tubulin synthesis are analyzed during ciliary regeneration of the ciliate Tetrahymena. Titration of the alpha-tubulin mRNA concentrations during the regeneration period reveal that enhancement of tubulin synthesis is preceded and accompanied by increased concentrations of tubulin mRNA molecules. Stimulation of tubulin synthesis is independent of the pool size of soluble tubulin molecules, as suggested by at least two independent lines of evidence: First, like cells of normal phenotype a temperature sensitive size mutant enhances tubulin synthesis as well as tubulin mRNA concentration during ciliary regeneration, although these large mutant cells have a much higher concentration and amount of soluble tubulin molecules in the cytoplasm. Second, slowly regenerating cells of normal phenotype shift-up their concentration of tubulin mRNA molecules already before a time, when ciliary outgrowth might cause a significant depletion of the pool of soluble tubulin molecules. Thus, neither an induction of tubulin synthesis nor an increase in tubulin mRNA molecules is mediated via changes in the pool size of soluble tubulin molecules.

Animals↗
PubMed1986

Post-meiotic DNA synthesis in nocodazole-blocked nuclei during conjugation of Tetrahymena thermophila. Induction of polyploidy in the micronucleus.

The formation of single, polyploid micronuclei was induced during conjugation of Tetrahymena thermophila with Nocodazole (ND) according to Kaczanowski et al. The increase in DNA content in these nuclei was measured cytophotometrically in conjugating pairs continuously exposed to the drug. ND-treated micronuclei ('restitution nuclei') undergo two complete rounds of DNA replication and enter the third at the time of pair separation. The DNA content of these micronuclei in late pairs was in the range 16-30C (mean 20C). This amount was similar to the sum of the DNA content of all post-meiotic products during normal conjugation at about the same stage. Thus the increase in DNA content in 'restitution' nuclei reflects some intrinsic ability of nuclei in pairing cells to replicate DNA independently of nuclear division.

Animals↗
PubMed1986

An estimation of the soluble tubulin content in Tetrahymena cells of normal and of size-altered phenotype.

The amount of soluble tubulin in a temperature-sensitive (ts) size mutant of the ciliate Tetrahymena was measured in a variety of physiological conditions. For this purpose a competitive ELISA assay for tubulin was set up. The assay is based on an antiserum against Tetrahymena axonemal tubulin. Characterization of the antiserum shows its mono-specificity towards tubulin as well as its potential to recognize tubulin from a wide variety of cellular sources and organisms. After fractionation of the cells into soluble material, cold-labile and cold-resistant structures, we found very little tubulin soluble (less than 20% of the total), while most of the tubulin is polymerized, especially into cortical structures. Prolonged starvation does not alter the tubulin content. During the culture growth cycle the percentage of the soluble tubulin increases. Growing the ts mutant at high temperature to a large cell size will also increase the pool of soluble tubulin to a large extent. Only under this condition is the amount of soluble tubulin about equal to that fixed in cilia. The tubulins in the three different compartments are polymorphic and have a different metabolism. This is indicated by the much higher specific activity of soluble tubulin compared with the structurally bound material. In agreement, the half-life of the soluble tubulin is shorter than that of the cortical tubulin.

Animals↗
PubMed1985

Analysis of a mutant expressing temperature-sensitive changes of cell size in Tetrahymena.

A temperature-sensitive mutant of Tetrahymena expresses an increase in cell volume by a factor of 2.5 upon shift to restrictive temperature. Cellular amounts of protein, RNA, and DNA increase at roughly the same proportions. The mutant cell size is attained by cessation of divisions immediately after temperature shift for a period of time which is about equal to one generation time. During this time cell growth and DNA replication continue at virtually unchanged rates. Maintained at the restrictive temperature the mutant cells divide at the same rate as the wild-type cells. Upon return to the permissive temperature, cell size is reduced by the combined effects of an accelerated division rate together with a decelerated growth rate.

Animals↗
PubMed1985

Deciliation interferes with cell-cycle progression in Tetrahymena.

The impact of ciliary regeneration upon cell-cycle progression of the ciliate Tetrahymena was studied. It was found that cell division ceases during ciliary regeneration, and starts again about 4 h after deciliation. Deciliation of an asynchronously multiplying culture results in a rapid interruption of DNA synthesis, followed by resumption 1 h later. This was shown by pulse-labelling the cells with [3H]thymidine at various times after deciliation. Cytophotometric determinations of the macronuclear DNA content substantiated these observations, since the average DNA content per cell remained constant within the first hour of regeneration, confirming the labelling experiments, after which it rose. At its maximum, the average DNA content was more than doubled as compared with the beginning of the experiment. This indicates that a substantial proportion of the regenerating cells performed two rounds of DNA replication prior to cell division. The massive drop in the average DNA content during the fifth hour after deciliation indicates that the culture becomes partly synchronized for cell division by the deciliation procedure. The division synchrony results from a greater delay of the next cell division when G2 cells are deciliated than occurs in G1 cells. This was shown by deciliating cultures of Tetrahymena thermophila cells in the respective stages of the cell cycle, which had been partly synchronized by elutriator centrifugation. Thus, deciliation followed by ciliary regeneration causes a varying degree of retardation in progression through the cell cycle, being greatest for G2 cells and least for G1 cells.

Animals↗
PubMed1984

Isolation and phenotypic characterization of Tetrahymena thermophila size mutants: the relationship between cell size and regulation of DNA content.

Temperature-sensitive size mutants of the ciliate Tetrahymena thermophila were selected following chemical mutagenesis. Phenotypical characteristics are given for seven cell lines, which have a range of average cell volumes from 8000 microns 3 to more than 100 000 microns 3. wild-type Tetrahymena cells have an average cell volume of 15 000 microns 3. Two of the mutagenized cell lines have comparatively small cells at 29 degrees C but normal cells at 37 degrees C; whereas the other five lines are normal at 29 degrees C but large at 37 degrees C. While the small cells are poor growers, the large cells grow excellently at 37 degrees C. Measurements of DNA, RNA and protein contents indicate a significant correlation between all parameters and cell size. However, since the cells tolerate considerably different concentrations of each class of macromolecules, the amount of any of these macromolecules cannot be tightly controlled by cell size.

DNA↗
PubMed1982

Mean macronuclear DNA contents are variable in the ciliate Tetrahymena.

Using cytophotometry the mean macronuclear DNA content of the ciliate Tetrahymena was found to be variable in two cell lines examined. While environmental changes (different culture fluids, temperature shifts) influence the mean DNA content of at least one of the two cell lines, spontaneous changes of the means are observed in both lines. The mean DNA contents of cultures maintained permanently in defined medium at various temperatures suggest the existence of a lower (7.5 pg) and an upper (13.6 pg) limit of the mean macronuclear DNA contents. Greatly differing means, either below or above those limits, were only occasionally found in cultures shifted to different temperatures for periods of less than 3 days. Eventually, the G2 mean macronuclear DNA contents of these cultures differed greatly from the doubled G1 mean value (maximum: mean G2 value equalling four times the G1 mean). Analysis of the maximum and minimum G1 DNA contents found in any culture indicates no absolute macronuclear DNA content triggering the regulation of macronuclear DNA content. There is no stringent correlation between the average cell volume and the average macronuclear DNA content. The data are discussed with reference to reported mechanisms of regulation of macronuclear DNA content.

Animals↗
PubMed1981

Molecular polymorphism of ciliary proteins from different species of the ciliate Tetrahymena.

Ciliary proteins from five different Tetrahymena species were analyzed by means of SDS-polyacrylamide gel electrophoresis. Of at least 32 different polypeptides, only 2 were found to have identical molecular weights in all species. In any comparison of 2 species, a maximum of 60% and at least 20% of the proteins had indistinguishable molecular weights, depending on the combination examined. Extensive codominance of ciliary proteins was found in a F1 hybrid. No interspecific cross-reactions occurred in double-diffusion tests involving the cilia from different species and antisera produced against them in rabbits.

Animals↗
PubMed1979

Increase in macromolecular amounts during the cell cycle of Tetrahymena: a contribution to cell cycle control.

Increases in RNA, protein and cell size were determined cytophotometrically during the cell division cycle of Tetrahymena. For these parameters different patterns were found. RNA accumulates slowly during G1 period and faster during macronuclear S. This agrees with the changing uridine incorporation rate which is at least partly related to the varying macronuclear DNA amount. Increases in protein content and cell size occur mainly during G1 and G2. This pattern was confirmed by determining the RNA : protein ratio in individual cells. It is minimal at the end of the G1 period. These findings and evidence from the literature suggest that initiation of DNA replication is under negative control by the relative RNA content of the cell.

Animals↗
PubMed1979

The regulation of amounts and proportions of genetic elements in the macronuclei of Tetrahymena thermophila strains of diverse karyotype.

Measurements of the micronuclear DNA content of clones with assumed different degrees of micronuclear ploidy confirmed the triploid nature of one clone. The micronuclear DNA content of a presumptive haploid clone was found to be slightly higher than expected, whereas one of two aneuploid clones had an unexpectedly low micronuclear DNA content. The macronuclear DNA content of cells with macronuclei which had developed from triploid, diploid and probably haploid and aneuploid macronuclear-Anlagen is very similar. Specifically, the smallest individual macronuclear DNA contents are consistently found within the same size class in all clones tested. Cell volumes, RNA and protein contents are alike in all clones tested. Only the growth rate and maximal density reached of one out of two aneuploid clones is reduced in comparison with the very similar other clones. The results are discussed with reference to the regulation of macronuclear DNA content, and to the compensation of gene-dosage.

Animals↗