Showing papers on "Melibiose published in 1982"

Isolation of the yeast regulatory gene GAL4 and analysis of its dosage effects on the galactose/melibiose regulon.

Abstract: GAL4 is a classically defined positive regulatory gene controlling the five inducible structural genes of galactose/melibiose utilization in yeast. The positive regulatory function of the GAL4 gene product in turn is controlled by the product of another gene, the negative regulator GAL80. We have cloned a 3.1-kilobase fragment containing GAL4 by homologous complementation using the multicopy chimeric vector YEp24 and demonstrated that multiple copies of GAL4 in yeast have pronounced dosage effects on the expression of the structural genes. Yeast transformed with GAL4-bearing plasmid become constitutive for expression of the galactose/melibiose genes, even in normally repressing (glucose) medium. Multiple copies of the GAL4 plasmid also increase expression of the structural genes in inducing (galactose) medium and can partially overcome the effects of a dominant super-repressor mutant, GAL80S. Using an internal deletion in GAL4, we have demonstrated that these dosage effects are due to overproduction of GAL4 positive regulatory product rather than an effect of the flanking sequences titrating out a negative regulator. These results point to the importance of competitive interplay between the positive and negative regulatory proteins in the control of this system. We have also used the dosage effect of GAL4 plasmid in combination with different GAL4 and GAL80 alleles to create new phenotypes. We interpret these phenotypes as indicating that (i) the repressing effects of glucose, at least in part, are mediated by the product of the negative regulatory gene, GAL80, and (ii) the GAL80 protein may have specific interactions with the control regions of the structural genes.

Isolation and preliminary characterization of the GAL4 gene, a positive regulator of transcription in yeast

Abstract: The GAL4 locus encodes a positive regulator of the inducible galactose and melibiose genes of yeast. Using the yeast plasmid vector YEp13, we have cloned GAL4 by complementation of a gal4 mutation. Restriction endonuclease mapping of subclone DNA has delimited the region sufficient for complementation to a 3.2-kilobase segment of DNA. The GAL4 mRNA is 2.8 kilobases long, sufficient to encode a protein as large as 105,000 daltons. The concentration of the GAL4 transcript is about 0.1 per cell and is almost identical in galactose-induced and noninduced cells. This result is consistent with a previously proposed model in which the activity of the GAL4 protein and not the transcription of the GAL4 gene is modulated by galactose induction.

Partial purification of galactinol synthase from leaves of Cucurbita pepo

Abstract: An enzyme synthesizing galactinol, UDP-D-galactose:myo-inositol-1-α-D-galactosyl transferase (galactinol synthase), has been isolated and partially purified from mature leaves of Cucurbita pepo. The enzyme showed optimal activity between pH 7.5 and 8.0 and required Mn2+ and the presence throughout isolation, storage, and assay of a sulfhydryl protectant (β-mercaptoethanol). EDTA was completely inhibitory. From a range of metal ions only Mg2+ partially replaced Mn2+, while Co2+, Zn2+, Cu2+, and Ni2+ were inhibitory. The uridine nucleotides and UDP-glucose were from 40 to 80% inhibitory and probably constitute part of the in vivo control system. High concentrations of galactose, melibiose, and xylose were partially inhibitory. The enzyme appeared highly specific for myo-inositol and showed no ability for galactosyl transfer to any other naturally occurring sugar or sugar alcohol. Some reactivity was obtained with the isomeric scyllo-inositol but the product was not identified. A range of other sugar nucleot...

The presence of an endogenous lectin in early embryos ofXenopus laevis.

Abstract: Xenopus laevis embryos were examined for the presence of endogenous carbohydrate binding proteins. Soluble extracts of cleavage, gastrula and neurula embryos are able to agglutinate trypsinized rabbit erythrocytes. Unlike other embryonic lectins this agglutination activity requires the presence of calcium ions but not of sulphydryl reducing agents. It is specifically inhibited by galactose and galactose containing derivatives. Thiodigalactoside is the most potent disaccharide inhibitor followed by lactose and melibiose respectively. Methyl α-D-galactopyranoside is a more effective inhibitor than its β anomer. N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, methyl α-D-mannopyranoside andL-fucose do not inhibit activity at concentrations at or above 25 mM. EDTA and EGTA are also strong inhibitors of this activity. β-D-galactoside binding lectins present in the early chick embryo have been implicated in cell to cell and cell to substrate adhesiveness of extraembryonic chick endoderm cells. Since cells of the blastula inXenopus laevis possess surface receptors bearing terminal β-D-galactoside groups it is possible that this β-D-galactoside binding lectin may play a role in the control of cell surface mediated events during development.

Occurrence and characterization of lympho-agglutinins in Indian plants.

Abstract: Lympho-agglutinins have been detected and characterized in 31 plant species. Out of these, 14 agglutinated only the neuraminidase-treated cells. The lectin-rich genera included Crotalaria and Erythrina (Fabaceae), Amaranthus (Amaranthaceae), Artocarpus (Moraceae) and Clerodendron (Verbenaceae). The new lectins varied in their potency and biological action spectra. The 3 Artocarpus species were found to be exceptionally potent and specific for melibiose, an alpha-D-galactoside. Among the most effective sugar inhibitors for other lectins were N-acetyl-galactosamine, lactose, galactose and asialofetuin/fetuin.

A new species of sterigmatomyces

Abstract: A new species of yeast——Sterigmatorayces fuzhouensis Yue was isolated from flower of mango in the public park of Fuzhou, Fujian province in 1978. The number of the sterimata (1—12 or more) is more than that in the other species. The daughter cell separates from the mother cell at the position near the end of the sterigma on the mother cell. The conidium is often pear-shaped or bottle-shaped just after separation. The streak on malt agar is cream colored, pasty, with a dry, dull and wrinkled surface. True mycelium presents in Dalmau plate cultures on corn meal agar. Occasionally septa can be found on mycelium. Single or clustered blastoconidia present on hypha and are similar to the mycotorula type of pseudomycelium. The present strain assimilates glucose, maltose, galactose, sucrose, lactose, raffinose, melibiose, sorbose, cellobiose, xylose, L-arabinose, D-arabinose, rhamnose, trehalose, ribose, ribitol, glucitol, galactitol, inositol, mannitol, erythritol, glycerol, ethanol, citric acid, and salicin cut not melezitose, α-methyl-D-glucoside, and lactic acid. Assimilation of potassium nitrate is in the negative. Since the strain we isolated differs from all hitherto described Sterigmatomyces species in either morphology or physiology, it is here considered as a new species. The diagnosis of the genus is extended to include the character of blastoconidium formation. A key to the genus has been given. The type culture is deposited in the Institute of Microbiology, Academia Sinica.

Isolation oftheyeast regulatory geneGAL4andanalysis ofits dosage effects onthegalactose/melibi

Abstract: GAL4isaclassically defined positive regulatory gene controlling thefive inducible structural genes ofgalactose/ melibiose utilization inyeast. Thepositive regulatory function of theGAL4geneproduct inturn iscontrolled bytheproduct of another gene, thenegative regulator GAL80. Wehave cloned a 3.1-kilobase fragment containing GAL4byhomologous comple- mentation using themulticopy chimeric vector YEp24 anddem- onstrated that multiple copies ofGAL4inyeast have pronounced dosage effects ontheexpression ofthestructural genes. Yeast transformed with GAL4-bearing plasmid become constitutive for expression ofthegalactose/melibiose genes, eveninnormally repressing (glucose) medium. Multiple copies oftheGAL4plasmid also increase expression ofthestructural genes ininducing (ga- lactose) medium andcanpartially overcome theeffects ofadom- inant super-repressor mutant, GAL80S. Using aninternal deletion inGAL4, wehave demonstrated that these dosage effects aredue tooverproduction ofGAL4positive regulatory product rather than aneffect oftheflanking sequences titrating outanegative regulator. These results point totheimportance ofcompetitive interplay between thepositive andnegative regulatory proteins inthecontrol ofthis system. Wehave also used thedosage effect ofGAL4plasmid incombination with different GAL4andGAL80 alleles tocreate newphenotypes. Weinterpret these phenotypes asindicating that (i) therepressing effects ofglucose, atleast in part, aremediated bytheproduct ofthe negative regulatory gene, GAL80, and(ii) theGAL80protein mayhave specific interactions with thecontrol regions ofthestructural genes. Awell-defined system for delineating aspects ofeukaryotic reg- ulation isthegalactose/melibiose utilization regulon inthe yeast Saccharomyces cerevisiae. TheGAL4geneinthis system encodes apositive regulatory protein required toexpress tran- scriptionally thestructural genes forgalactose/melibiose me-