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Biomedical subjects

H Amstutz

Publications and source records attributed to H Amstutz.

31 records · Page 2Linked to original sources
PubMed1986

Functional complementation between mutations in a yeast suppressor tRNA gene reveals potential for evolution of tRNA sequences.

Successive rounds of mutagenesis of a Schizosaccharomyces pombe strain bearing the UGA-reading sup3 tRNASer suppressor have been carried out for two cycles of inactivation and reactivation of the suppressor. The suppressor phenotype at each stage was found to involve different combinations of three mutations, A30, A53, and A67, in the sup3-UGA gene. Single mutations A30 and A53 inactivate the suppressor as does the presence of all three mutations. A67 by itself is phenotypically neutral, but in combination with either A30 or A53 suppressor function is restored. The frequency with which these and other complementation events occur in S. pombe demonstrates a significant potential for nucleotide sequence evolution in tRNA. Differential expression of the S. pombe genes in Saccharomyces cerevisiae suggests that the two yeasts have diverged at the transcriptional and RNA processing level. Processing of the mutant tRNA precursors in S. cerevisiae reveals a hierarchy of structural domains within the tRNA that vary in their importance for RNase P cleavage.

Alleles↗
PubMed1986

Analysis of centromeric DNA in the fission yeast Schizosaccharomyces pombe.

The Schizosaccharomyces pombe centromere-linked genes, LYS1 and CYH1 on chromosome I and TPS13 and RAN1 on chromosome II, have been isolated. The genetic order of these markers with respect to their centromeres was determined to establish relative directionality on the genetic and physical maps. Chromosome walking toward the centromeres reveals a group of repetitive sequences that occur only in the centromere regions of chromosomes I and II and at one other specific location in the S. pombe genome, presumably the centromere of chromosome III. The major class of large repeated sequence elements is 6.4 kilobases (kb) long (repeat K), portions of which occur at least twice on chromosome II and in several tandemly arranged intact copies at another centromeric location. Repeat K in turn contains groups of smaller repeats. Genetic recombination is strongly suppressed in the centromere II region, which contains at least 30 kb of repeated sequences. Centromeric DNA organization is much more complex in fission yeast than has been described in budding yeast (Saccharomyces cerevisiae), possibly because of the larger more condensed nature of the S. pombe chromosomes.

Base Sequence↗
PubMed1985

Concerted evolution of tRNA genes: intergenic conversion among three unlinked serine tRNA genes in S. pombe.

In many cases the multiple genes coding for one specific tRNA are dispersed throughout the genome. The members of such a gene family nevertheless maintain a common nucleotide sequence during evolution. A major mechanism contributing to this concerted evolution is intergenic conversion. Here we show that it occurs between three tRNA genes of related sequence residing on different chromosomes of Schizosaccharomyces pombe. Sequence analysis of converted genes indicates that blocks of a minimal length of 18-33 bp and of a maximal length of 190 bp can be transferred from one gene to the other. During meiosis the frequency of these transfers lies in the order of 10(-5) per progeny spore. Information transfer between any two members of the gene family occurs in both directions.

Anticodon↗
PubMed1981

Friction and wear properties of polymer, metal, and ceramic prosthetic joint materials evaluated on a multichannel screening device.

A 12-channel wear screening device was used to compare the wear properties of a variety of prosthetic joint materials. Two types of tests were run: (1) Ultrahigh molecular weight (UHMW) polyethylene bearing against metal or ceramic counterfaces and (2) various polymers bearing against 316 stainless steel as a standard counterface. Wear was quantified by weighing the polymer specimens, with presoaking and control-soak specimens used to minimize the error due to fluid absorption. The specimens were lubricated with bovine blood serum. Friction and polyethylene wear was very low with each of the metals (316 stainless steel, cobalt-chrome alloy, multiphase alloy, and titanium 6-4 alloy) such that the differences in wear rate would not be significant in terms of choosing a material for clinical application. However, titanium 6-4 alloy was found to be especially susceptible to abrasive wear by particles of acrylic cement. Nitrided titanium 6-4 counterfaces were impervious to acrylic abrasion. Polyethylene wear against highly polished, fully dense ceramics (Sialon, Alumina, Macor, and pyrolytic graphite) was as low as that with the metal counterfaces. Wear increased slightly with increasing ceramic surface roughness. The coefficient of friction of polyethylene against pyrolytic graphite was two to three times higher than with the metals or other ceramics. All of the alternate polymers underwent more wear than UHMW polyethylene. Teflon and polyester, two polymers that have proven unsuccessful in prior clinical use, had wear rates 1,600 and 830 times greater than polyethylene, respectively, an indication that the laboratory wear test provided a quantitative prediction of the behavior of the materials in vivo. However, it was difficult to assess the clinical significance of the less extreme wear rates since the ability of the tissues encapsulating a prosthesis to accomodate wear debris is not known on a quantitative basis.

Animals↗
PubMed1976

T lineage lymphocytes in nude mice born from homozygous nu/nu parents.

T lineage cells are found in the spleen of neonatal nu/nu mice born from nu/nu x nu/nu matings, and also in old, healthy nude mice obtained from the usual nu/+ x nu/nu matings. Their presence in neonatal nude mice which were never in contact with mother or normal littermate thymus products shows that commitment of stem cells towards the T lineage does not require the influence of the thymus.

Aging↗