Search PubMed⌕ Search

Biomedical subjects

R K Mortimer

Publications and source records attributed to R K Mortimer.

65 records · Page 4Linked to original sources
PubMed1968

Use of nystatin to eliminate spontaneous revertants in yeast.

Studies of induction of suppressor mutants may be obscured by revertants already present in the treated population. Such revertants, which appear as a minority of prototrophs among auxotrophs, can be eliminated by pretreatment with nystatin before application of the mutagen. Treatment with nystatin, under the proper conditions, decreased the frequency of prototrophs about 30-fold. This is sufficient for studying induced mutation at frequencies close to the spontaneous frequency.

Mutagens↗
PubMed1966

Unsaturated fatty acid mutants of Saccharomyces cerevisiae.

Resnick, Michael A. (University of California, Berkeley), and Robert K. Mortimer. Unsaturated fatty acid mutants of Saccharomyces cerevisiae. J. Bacteriol. 92:597-600. 1966.-The wild type of the yeast Saccharomyces cerevisiae does not require fatty acids or sterols for growth. Two types of lipid nutritional mutants have been induced in this organism. One of these classes of mutants requires an unsaturated fatty acid and is associated with a locus on chromosome VII. The other class of mutants needs either an unsaturated fatty acid or ergosterol for growth. Experiments involving identification and characterization of these mutants are presented.

Chromosome Mapping↗
PubMed1966

Yeast genetics.

Explore the source record for details and available documents.

Genetics↗
PubMedDate not supplied

Isolation of a DNA fragment that is expressed as an amber suppressor when present in high copy number in yeast.

A plasmid carrying a DNA sequence conferring amber suppression has been isolated from yeast pool 35 DNA. The plasmid YEp13-SUP suppresses the amber mutations rad50-1 and trp1-289 as well as other known amber mutations. This sequence is located on the 2.5-kb insert and is expressed only when the plasmid bearing it is present in high copy number. The suppressor sequence was shown to integrate close to the MAL4 gene located on the right arm of chromosome XI.

Base Sequence↗
PubMedDate not supplied

An endomitotic effect of a cell cycle mutation of Saccharomyces cerevisiae.

A recessive temperature-sensitive mutation of Saccharomyces cerevisiae has been isolated and shown to cause an increase in ploidy in both haploids and diploids. Genetic analysis revealed that the strain carrying the mutation was an aa diploid, although MNNG mutagenesis had been done on an a haploid strain. When the mutant strain was crossed with an alpha alpha diploid and the resultant tetraploid sporulated, some of the meiotic progeny of this tetraploid were themselves tetraploid, as shown by both genetic analysis and DNA measurements, instead of diploid as expected of tetraploid meiosis. The ability of these tetraploids to continue to produce tetraploid meiotic progeny was followed for four generations. Homothallism was excluded as a cause of the increase in ploidy; visual pedigree analysis of spore clones to about the 32-cell stage failed to reveal any zygotes, and haploids that diploidized retained their mating type. An extra round of meiotic DNA synthesis was also considered and excluded. It was found that tetraploidization was independent of sporulation temperature, but was dependent on the temperature of germination and the growth of the spores. Increase in ploidy occurred when the spores were germinated and grown at 30 degrees, but did not occur at 23 degrees. Two cycles of sporulation and growth at 23 degrees resulted in haploids, which were shown to diploidize within 24 hr when grown at 30 degrees. Visual observation of the haploid cells incubated at 36 degrees revealed a cell-division-cycle phenotype characteristic of mutations that affect nuclear division; complementation analysis demonstrated that the mutation, cdc31-2, is allelic to cdc31-1, a mutation isolated by Hartwell et al. (1973) and characterized as causing a temperature-sensitive arrest during late nuclear division. The segregation of cdc31-2 in heterozygous diploids was 2:2 and characteristic of a noncentromere-linked gene.

Cell Cycle↗