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11.
A Genetic Analysis of CANDIDA ALBICANS: Isolation of a Wide Variety of Auxotrophs and Demonstration of Linkage and Complementation 总被引:20,自引:1,他引:19
Naturally occurring strains of Candida albicans appear to be diploid and heterozygous for a limited number of nutritional markers. Additional heterozygosity can be induced by treatment with mutagens; nitrous acid alone or in combination with UV is a potent mutagen in terms of both efficacy and efficiency in the production of a wide variety of mutations. Spheroplast fusion followed by regeneration on selective media revealed complementation among four histidine-requiring mutants analyzed. Some of the fusion products appeared to be stable prototrophs, whereas in others several kinds of segregants resulted, apparently due to chromosomal or nuclear elimination. The results are suggestive of both heterokaryosis as well as nuclear fusion. The procedures described can be successfully used for generating new mutants and studying allelism. Three sets of linkage relationships have been derived from evidence provided by concomitant appearance or cosegragation of several auxotrophic markers. 相似文献
12.
Multivalent Repression of Isoleucine-Valine Biosynthesis in Saccharomyces cerevisiae 总被引:7,自引:3,他引:4 下载免费PDF全文
Regulation of the biosynthesis of four of the five enzymes of the isoleucine-valine pathway was studied in Saccharomyces cerevisiae. A method is described for limiting the growth of a leucine auxotroph by using valine as a competitor for the permease. Limitation for isoleucine and valine was accomplished by the use of peptides containing these amino acids conjugated with glycine as nutritional supplements for auxotrophs. The enzymes were repressed on synthetic medium containing isoleucine, valine, and leucine, as well as on broth supplemented with these amino acids. Limitation for any of the three branched-chain amino acids led to derepression of the isoleucine-valine biosynthetic pathway. Maximal derepression ranged from 3-fold for threonine deaminase to approximately 10-fold for acetohydroxyacid synthase. (Two of the enzymes, acetohydroxyacid synthase and dihydroxyacid dehydrase, may be controlled by a mechanism different from that regulating threonine deaminase.) Possible molecular mechanisms for multivalent repression are discussed. 相似文献
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Correlation between polyploidy and auxotrophic segregation in the imperfect yeast Candida albicans. 下载免费PDF全文
In order to clarify the relationship between polyploidization and the capability of phenotypic switching in the imperfect yeast Candida albicans, two types of variants were isolated as segregants from a fusant, which produced a proportion of the cell population with a higher ploidy than the rest, either in a temperature-dependent or -independent manner, when incubated at low (28 degrees C) and high (37 degrees C) temperatures. In the case of the temperature-dependent type of variants, high-ploidy cells appeared at 37 degrees C but rarely at 28 degrees C. This phenotype was named Pldts (temperature-sensitive polyploidization), and the temperature-independent phenotype was called Pld-. The appearance of high-ploidy cells in the culture of the Pldts strain at 37 degrees C was accompanied by a significant increase in the frequency of auxotrophic variants; these variants probably occur as a result of segregation of auxotrophic markers from the heterozygous to the homozygous state. Both Pldts and Pld- phenotypes were recessive in a fusion with a Pld+ parent. An adenine auxotrophic marker (ade1) was introduced into a Pldts strain in a heterozygous state, and the individual high-ploidy cells of this strain, grown at 37 degrees C, were micromanipulated to form colonies, which consisted of red and white sectors appearing at high frequency on a pink background. When the ade1 auxotrophy was introduced into Pld- strains, frequently sectored colonies were produced. These results suggested an increased level of chromosome missegregation in both types of Pld mutants. Analyses by pulsed-field gel electrophoresis of Ade-segregants, derived from a micromanipulated high-ploidy cell of a Pld(ts) strain, suggested the occurrence of nonreciprocal recombination, some of which includes chromosome loss. 相似文献
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The antimetabolite sulfanilamide inhibits sporulation in Saccharomyces cerevisiae strain AP1. Cells exposed to sulfanilamide at various times during the sporulation process become progressively insensitive to the drug, although accumulation of sulfanilamide by the cells increases with time. Vegetative growth of AP1 is practically unaffected by sulfanilamide; pregrowth of the cells in the presence of the drug does not prevent sporulation. Thus, inhibition is confined to the meiotic phase of the cell cycle. Sensitivity to sulfanilamide is independent of pH. Increasing the time cells are exposed to sulfanilamide results in a progressive reduction of ascus formation; however, the inhibition is reversible since sporulation can occur in cells exposed to the drug for greater than 24 h. The drug arrests the cells at a point before commitment to sporulation, since yeast cells exposed to sulfanilamide for 12 h do not complete the sporulation process when returnedto vegetative medium, but resume mitotic growth instead. Meiotic nuclear division is largely prevented by sulfanilamide, and synthesis of RNA and protein is severely retarded. DNA synthesis is inhibited up to 50%; glycogen synthesis is approximately 90% inhibited. Other yeast strains showed varying sensitivity to sulfanilamide; homothallic strains were generally less affected. 相似文献
17.
The cadherin family of cell-cell adhesion molecules is turning out to be much more diverse than previously thought, with members involved in several kinds of intercellular junctions. The adhesive specificity and cytoskeletal interaction of these members varies. Their cytoplasmic terminals are specialized for binding several families of 'mediator' proteins which interconnect to the actin or intermediate filament systems. These multi-molecular complexes have roles not only in cell-cell adhesion, but also in intracellular signalling of developmental information. 相似文献
18.
Summary Histochemical studies performed on specimens of intestine from 12 to 37-week human foetuses showed that the epithelial glycoproteins of the goblet cells of the small intestine are non-sulphated sialoglycoproteins containing neutral sugar (hexose, 6-deoxy hexose or N-acetyl hexosamine residues with Periodic acid-Schiff (PAS) reactive vicinal diols), sialic acids without O-acyl substituents, smaller and variable quantities of sialic acids with O-acyl substituents at positions C8 or C9 (or with two or three side chain substituents) and O-acyl sugars (neutral sugars with an ester substituent blocking PAS reactivity). In the lower small intestine glycoproteins containing 8 (or 9)-O-acyl sialic acids are first observed in goblet cells at the tips of the villi. As the foetus matures their quantity increases and they are found in goblet cells located along the length of the villi. Smaller quantities of O-acyl sialic acids and traces of O-acyl sugars occur in the goblet cells of the upper small intestine. The colonic goblet cells contain sulphosialoglycoproteins of two types. The first type, found in the majority of specimens, contains O-sulphate ester, neutral sugar, O-acyl sugars and 8 (or 9)-O-acyl sialic acids. The second type contains O-sulphate ester, neutral sugars, and sialic acids which are either without side chain O-acyl substituents or are a mixture of such acids and 8 (or 9)-O-acyl sialic acids; O-acyl sugars are reduced or absent. The degree of sulphation of the foetal colonic goblet cell epithelial glycoproteins differs with the region of the colon, the level of the crypt and the gestational age of the foetus in a manner consistent with that described by Lev & Orlic (1974). The detection of O-acyl sugars in foetal intestinal glycoproteins adds to the known examples of such sugars and strengthens the suggestion that they are a normal constituent of colonic epithelial glycoproteins.Part of this work was presented at the 32nd meeting of the Canadian Federation of Biological Sciences, Calgary, Alberta, June 1989 (abstract # 336). 相似文献
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O-Glycosidic analogs of N-acetylglucosamine are good substrates for galactosyltransferase, and as the O-substituted group becomes more hydrophobic, the apparent Km decreases as much as 2000-fold. l-leucine, leucine-amide, norleucine, valine, ?-amino-n-caproic acid and tyrosine-agaroses all retain galactosyltransferase in the presence of 1.25 m ammonium sulfate. The enzyme is eluted quantitatively with a five- to tenfold purification by a decreasing linear gradient of ammonium sulfate. Galactosyltransferase was not specifically bound on any of a series of ω-aminoalkylagaroses tested. A simple and highly efficient procedure for the isolation of galactosyltransferase from bovine skim milk was developed and consisted of a 40–60% ammonium sulfate precipitation of the enzyme from skim milk followed by chromatography on (1) norleucine-Sepharose, (2) UDP-hexanolamine-Sepharose, and (3) α-lactalbumin-Sepharose. 相似文献