Gertrude Lindegren

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.

The genetics of melezitose fermentation in Saccharomyces

SummaryA multiple series of alleles of the gene MZ exist inSaccharomyces. The members of this series are differentiated from one another by their adaptive response to maltose, turanose, sucrose, melezitose and alpha-methyl glucoside. The more capable members of the series can ferment all five sugars while various multiple alleles are characterized by loss of ability to act on alpha-methyl glucoside, melezitose or sucrose. MZ is linked to the gene MA which controls the production of a specific maltase and to the gene MG which controls the production of a specific alpha-methyl glucosidase. All members of the series of multiple alleles produce the same enzyme showing that the gene and the enzyme are not identical. The enzyme is produced in three different steps, the initial one being a specific reaction of gene with substrate and the final one being a non-specific elicitation of enzyme.

Chromosome mapping of linkage data fromSaccharomyces by tetrad analysis

In yeast tile diploid zygote is formed by the copulative fusion of two haploid cells of opposite mating-type, a and a. When the zygote sporulates, four haploid spores are formed in a single sac and a single chromatid from each set of chromosomes eventually passes into each spore. Thus gene-pairs in a heterozygote segregate in a 2 : 2 ratio (the regular Mendelian ratio) in the ascus. Hybrids can be obtained in which the segregation of many different combinations of genes may be observed simultaneously. Segregation in the ascus of gene-eontrolledphenotypes, which correspond to chromosomal regions containing the specific genes, yields information concerning the location of genes. This method is known as tetrad analysis. Since a tetrad represents al l /our chromatids resulting from the same meiosis, tetrad analysis possesses certain obvious advantages over conventional Mendelian analysis in which only one of the four chromatids of each meiosis is collected. Chromosome maps locating thirteen genes (table 1) on seven different chromosome arms (fig. 10) have been constructed utilizing the five types of distributions discussed below. The genes 0c, ad, an, ga, hi, th, and ur were first described and established as ~gular Mendelian

Genetical analysis of the clones from a single tetrad of saccharomyces showing non-Mendelian segragation

SummaryA single tetrad in which one genetical marker had segregated irregularly was analyzed genetically by outcrossing each culture derived from the tetrad to other haploid clones. Regular segregation in the resultant hybrids indicated that the cultures were all haploid. The original ascus was tetratype proving that all four nuclei had survived after reduction. All clones were haploid proving that the irregularities could not have arisen from fusion following an extra mitosis. It is inferred that the extra recessive was the result of an interaction in the hybrid in which a dominant was converted into a recessive allele. The converted clone was identified by the intermediate character of its physiological activity.

Sporulation in Saccharomyces cerevisiae

1. Sporulation in Saccharomyces cerevisiae is influenced by the genetic constitution of the culture as well as by the composition of the nutrient medium. A specific nutrient medium which gives maximum sporulation has been developed and described. 2. On this medium, heterozygous, legitimately diploid cultures produce an abundance of viable 4-spored asci. Single ascospore cultures (which may be either illegitimately diploid or haploid) sporulate much more irregularly; some do not sporulate at all. The asci from single ascospore cultures generally contain only one or two spores, and their viability is much diminished. 3. A survey of forty commercial baking yeasts was made. Some were legitimately diploid, while others were of single ascospore origin.

Oxidative detoxication of thallium in the yeast mitochondria.

When yeast cells are grown in thallium-containing broth, the thallium ion is oxidized in the mitochondria to Tl2O3. This oxide is subsequently discharged from the mitochondria and finally excreted from the protoplast.

Staining yeast cells for electron microscopy by growth in copper-containing nutrient broth

Copper attaches to the nucleoli and the chromosomes of yeast cells. Lindegren and Zink (1969) showed that lipolated mitochondria contain fat and inferred that fat was an energy source. The present study shows that fat is present in the nucleolus and fat is inferred to be an energy source for nucleolar metabolism. The extrusion of nucleoprotein from the nucleolus into the cytoplasm is demonstrated for the first time by electron microscopy. The copper-stained chromosomes are about 90 å in diameter and tightly packed in the nuclear vacuole.

Gene controlled resistance and sensitivity to caffeine and nicotine in Saccharomyces.

SUMMARY: A significant extension in the variety of gene-markers available in Saccharomyces has been achieved by exploiting resistance and sensitivity to a variety of poisons. Although resistance to many poisons was obviously heritable, gene-control could not be demonstrated, presumably because other genes modified the phenotypes. Gene-control of resistance and sensitivity for both nicotine and caffeine was demonstrated by tetrad analysis and by the observation of regular Mendelian segregation of the characters among the progeny of closely related hybrids.

Environmental and Genetical Variations in Yield and Colony Size of Commercial Yeasts

One essential requirement of a good commercial bakers yeast is the ability to transform the maximum amount of nutrients in the fermentor into yeast in the shortest possible time. Yeasts vary in this property, and our first step in an attempt at yeast improvement included the collection of various strains, and the design of adequate tests for selecting the high-yielding ones. This yield test was designed primarily to reject inferior cultures. The early data are comparative and indicative rather than absolute. In handling hundreds of cultures in the laboratory it is not feasible to duplicate plant conditions, and yields of the same yeast are relatively lower in the test-tube than in the plant. Our ultimate objective is to devise a test which will predict accurately the behavior of a yeast under plant conditions.