Maurice Ogur

The nucleic acids in a polyploid series of Saccharomyces.

Abstract 1. 1. A polyploid series from haploid through tetraploid in yeasts has been analyzed for a number of cellular characters including dry weight, desoxyribonucleic acid (DNA), ribonucleic acid (RNA), and metaphosphate content. 2. 2. The DNA content per cell is found consistent with an integral ratio in the polyploid series, and this character has proved most reliable of those studied in estimating ploidy. 3. 3. Dry weight, RNA, and metaphosphate content per cell are also ploidy-dependent but vary over a wider experimental range. 4. 4. The reliable estimation of ploidy in yeast provides a critical tool for the analysis of irregular segregation in the yeasts.

Tricarboxylic Acid Cycle Mutants in Saccharomyces: Comparison of Independently Derived Mutants

A yeast mutant independently isolated as a glutamate auxotroph (glt2-1) was similar to the glt1-1 mutant in exhibiting a blocked tricarboxylic acid cycle due to the lack of aconitate hydratase. The new mutant differed by exhibiting blocks in lysine and cytochrome biosynthesis which segregated together with the glutamate requirement.

Respiration in a polyploid series in Saccharomyces

Abstract 1. 1. A polyploid series from haploid through tetraploid in Saccharomyces has been analyzed for respiration and aerobic fermentation with glucose as substrate. 2. 2. Q O 2 (cell) and Q CO 2 air (cell) increase in integral fashion with ploidy in cultures grown under comparable conditions. 3. 3. Respiration-sufficient hybrids with one respiration-deficient parent exhibit the full ploidy-dependent respiration of the hybrid. 4. 4. The findings are interpreted as dependence of quantitative enzyme potential on the quantitative genetic complement.

Inhibition of yeast Δ1-pyrroline-5-carboxylate dehydrogenase by common amino acids and the regulation of proline catabolism

Abstract A yeast glutamate auxotroph (glt1 − 1), blocked in the tricarboxylic acid cycle at aconitase, is shown to possess catabolic pathways to glutamate from proline, arginine and glutamine, and grows on any of these amino acids in a minimal medium. This mutant does not, however, grow on these amino acids in a medium containing the full complement of common amino acids minus glutamate. The mechanism of this growth failure involves partial inhibition of the catabolic routes to glutamate by more than half the common amino acids. In the case of proline catabolism, this inhibition is localized principally at the enzyme Δ1-pyrroline-5-carboxylate: NAD(P)+ oxidoreductase by in vitro studies. Similar results with this enzyme prepared both from yeast and from beef kidney mitochondria suggest that the inhibition observed may be the basis of a regulatory mechanism of general significance.

The isolation and characterization of a Saccharomyces mutant deficient in Δ1-pyrroline-5-carboxylate dehydrogenase activity

Abstract 1. Clones failing to grow on proline were isolated after ethylmethane-sulfonate treatment of a glutamate auxotroph of Saccharomyces, originally capable of utilizing proline as principal nitrogen source. 2. Most of the non-utilizers of proline were cytochromeless. One, however, possessed normal cytochrome levels but lacked Δ1-pyrroline-5-carboxylate dehydrogenase activity. This is the first isolate of this lesion in Saccharomyces.

Demonstration by cellular nitrogen and turbidity of the haploid state of the four clones of yeast derived from an irregularly segregating locus

Demonstrations (WINGE, 1935 ; LINDEGREN and LINDEGREN, 1951 ; TOWNSEND and LINDEGREN, 1954; OGUR, MINCKLER, LINDEGREN and LINDEGI~EN, 1952; OGOR, 1954; OGUR, in press) that size and a var iety of size-related characteristics are ploidy dependent in Saccharomyces make possible their application as criteria of ploidy in genetical analyses. One may either substantiate or exclude polyploid segregation as the possible origin of an irregularly segregating ascus by establishing the degree of ploidy of the single aseospore clones derived from the ~scus. i Twenty-four-hour nutrient, agar slants of the four clones derived from the irregularly segregating ascus described by LINDEGREN et al. in the preceding paper were each inoculated into 40 ml of 2 per cent glucose complete medium and shaken for 15 hours at 30 ~ C. Cells were harvested and washed 3 times With cold distilled water. Cell suspensions were diluted to a turbidity ca. I00 by the KlettSummerson photo-electric colorimeter using the blue (420ran) filter. Cell numbers were scored directly in a hemacytometer. Total

Direct experimental observation of cells in phenomic lag.

By employing cells mutating at a very high spontaneous rate and a grid plate containing a medium totally selective against mutant cells, direct microscopic observation was made of mutant cells of recent origin passing through a limited number of phenomic lag divisions.