Concanavalin A binds to puffs in polytene chromosomes

Glycoproteins with N-acetylglucosamine and mannose residues in Chinese hamster metaphase chromosomes

Distribution of glycosylated proteins in Chinese hamster metaphase chromosomes was studied with fluorescein isothiocyanate conjugated lectins. Three substructural domains with distinct glycoprotein compositions were identified. In situ binding of the lectins Wheat germ agglutinin (WGA) and Datura stramonium agglutinin (DSA) showed that chromosomal proteins containing N-acetylglucosamine residues preferentially localize to the surface domain and the helically coiled substructure of chromatids. In Western blots, digoxigenin conjugated WGA and DSA bound to several chromosomal proteins with molecular weight ranges of 45-220 kD and 66-220 kD, respectively. Binding of Galanthus nivalis agglutinin revealed that mannosylated chromosomal proteins are enriched at the surface and G/Q band domains, and their molecular weights range from 97 to 200 kD. The carbohydrate side chain structure of these mannosylated proteins must be quite specific, as after binding of another mannose-specific lectin, Concanavalin A, only a faint fluorescence was observed in metaphase chromosomes and only one protein band of 185 kD was weakly stained in Western blots. These data suggest that chromosomal glycoproteins containing N-acetylglucosamine and mannose residues play a role in the higher order structural organization of metaphase chromosomes.

Comparison of sequences of a transcriptional coactivator MBF2 from three Lepidopteran species Bombyx mori, Bombyx mandarina and Samia cynthia

MBF2 was first isolated from the silkworm Bombyx mori as a positive cofactor that activates transcription through its interaction with TFIIA. To identify conserved domain(s) within the MBF2 molecule, we isolated cDNAs encoding MBF2 homologues from other silkworms Bombyx mandarina and Samia cynthia. Bacterially expressed and purified MBF2 of B. mandarina and S. cynthia activated transcription in vitro. The predicted amino acid sequences of MBF2 from two Bombyx species share 97% homology. When we compared between B. mori and S. cynthia factors, the homology reduced to 50%. Four regions in MBF2 are conserved among these three species. Two of them are present in the middle region of MBF2 that is essential for the transcriptional activation.

Age-related patterns of lectin-binding nuclear glycoproteins of hamster liver

We studied the age-related patterns of lectin-binding liver nuclear glycoproteins from hamsters between 5 and 35 weeks of age. The examinations of the carbohydrate structures of liver nuclear glycoproteins in relation to the age of hamsters were carried out after electrophoresis and blotting by a very sensitive immunological detection system with highly specific digoxigenin-labelled lectins. The results reported in the present study do not show any significant changes in the patterns of nuclear glycoproteins with regards to the age of hamsters except the decrease in affinity of wheat germ agglutinin (WGA) to 63 kDa glycoprotein bearing single O-linked N-acetylglucosamine residues.

Fucosylated glycoproteins in Chinese hamster metaphase chromosomes

Distribution of fucosylated proteins in Chinese hamster metaphase chromosomes was studied with a fluorescein isothiocyanate conjugated monofucosyl-specific lectin, Ulex europaeus agglutinin I (UEA I). In situ binding of UEA I showed that fucosylated chromosomal proteins are preferentially localized to two internal structural domains of metaphase chromosomes: the helically coiled substructure of chromatids, and the Q-band regions. Corresponding proteins were identified in Western blots of isolated metaphase chromosomes. Several proteins with molecular weights ranging from 33 to 195 kD were recognized by UEA I. These data suggest that a subset of chromosomal proteins are fucosylated; they may have a role in the structural organization of chromosomes.

Glycosylation of chromosomal proteins: localization of O-linked N-acetylglucosamine in Drosophila chromatin

Drosophila polytene chromosomes contain a surprisingly large amount of terminal N-acetylglucosamine (GlcNAc) residues along their lengths, as determined by staining with a fluorescently tagged lectin, wheat germ agglutinin (FITC-WGA) and by specific radio-labeling with bovine galactosyltransferase and UDP-[3H]galactose. FITC-WGA intensely stains polytene chromosomes in a distinctive banding pattern in which condensed chromatin is brightly labeled and transcriptionally active "puff" regions are less intensely stained. Biochemical analyses of galactosyltransferase-radiolabeled chromatin indicates that nearly all of the chromatin-associated GlcNAc moieties exist as single monosaccharide residues attached to protein by an O-linkage (O-GlcNAc). Chromatin is enriched in O-GlcNAc (over 400 pmol/micrograms of chromatin protein) as compared with total nuclei and other cellular compartments. O-GlcNAc moieties are found on a myriad of chromatin proteins that have diverse types of intermolecular associations with other nuclear components.

Characterization of glycoconjugates in an embryonic human epithelial line and changes consequent to adaptation to a hyperosmotic medium

Cell surface and cytoplasmic glycoconjugates were characterized in embryonic human explant cells (a transformed heteroploid line) cultured in iso-osmotic medium (0.137 M NaCl) and in hyperosmotic medium (0.274 M NaCl) for 10 days in order to study the changes induced in these compounds by hyperosmoticity. Cytochemical and ultracytochemical staining selective for glycoconjugates was carried out. The following results were obtained: (1) glycoproteins, glycosaminoglycans and glycolipids are present on the cell surface and in the cytoplasm of the explant cells; (2) lectin histochemistry combined with glycosidase digestion demonstrated the presence of the disaccharides fucose-N-acetylglucosamine and sialic acid-beta-galactose as terminal sequences; (3) histophotometric evaluation of lectin labelling showed a noticeable decrease in histochemical reactivity of adapted cells; (4) plasma membrane cell coat decreased in adapted cells, which was emphasized by ultracytochemical reactions and a rearrangement of glycolipids in the cytoplasm.

O-glycosylation of eukaryotic transcription factors: implications for mechanisms of transcriptional regulation

Glycosylation is often regarded as being restricted to proteins confined to the cell surface or within the lumen of intracellular organelles. Here we show that the human RNA polymerase II transcription factor Sp1 bears multiple O-linked N-acetylglucosamine (GlcNAc) monosaccharide residues. The lectin wheat germ agglutinin specifically inhibits the transcriptional activation but not the DNA binding function of Sp1. Furthermore, many other RNA polymerase II transcription factors also bear terminal GlcNAc residues, whereas most nuclear proteins, including RNA polymerase I and III transcription factors tested, do not. In some cases, only a subset of the polypeptide species within a particular family of closely related RNA polymerase II factors appears to be glycosylated. Our findings raise the possibility that O-linked GlcNAc residues play a role in the mechanism or regulation of transcriptional activation of RNA polymerase II.

Specific binding of lectins with the nucleus of the sea urchin embryo and changes in the lectin affinity of the embryonic chromatin during the course of development

(1) Embryonic cells of sea urchins were made permeable by treating them with glycerol solution for the purpose of allowing penetration of macromolecules into the cell. With the use of such permeabilized cells, several kinds of fluorescent dye-labeled lectins were introduced into the cell, and it was found that some lectins showed notable affinity with the nucleus as compared with cytoplasmic structures. (2) Isolated chromatin was incubated with several kinds of fluorescent dye-labeled lectins in vitro, and the amount of lectins bound with the chromatin was measured by fluorometry. By means of this method, the lectin-binding capacity of chromatin was estimated and compared at various stages of development. It was found that lectins could be classified into three groups according to the mode of binding with the chromatin: (a) Extent of binding increased notably at the gastrula stage (Con A and RCA-120); (b) extent of binding showed a temporary decrease at the gastrula stage (TTA); and (c) very low level of binding was maintained throughout all stages, and no particular change was observed at any stage of development (WGA, SBA, and UEA-I). (3) These facts seem to suggest that lectin-binding components are contained in sea urchin chromatin, and that drastic changes occur in these components of chromatin at the stage of gastrulation. It was proposed that the lectin-binding components such as proteoglycans and glycoproteins may play regulatory roles in embryonic chromatin at early stages of development.

Selective exposure of antigenic determinants in chromosomal proteins upon gene activation in polytene chromosomes

The immunological accessibility of the nucleosomal core protein H3 and non-histone protein, HMG-1, was studied in transcriptionally active regions of Chironomus thummi polytene chromosomes. Chromosomal loci were decondensed by incubating isolated salivary glands in various salt solutions or hemolymph. Indirect immunofluorescence studies on these chromosomes using anti-sera to histone H3 revealed that the puffed regions were depleted of fluorescence. The lack of fluorescence could be correlated with the degree of puffing and the level of transcriptional activity. The puffed regions fluoresce after anti-H3 addition if the chromosomes are not cross-linked with formaldehyde, and if prior to the addition of antibodies the chromosomes are treated with 45% acetic acid. We conclude that, whereas histone H3 is present in the puffed regions, its antigenic determinants are sterically hindered by components which are extractable by 45% acetic acid. On the other hand, the antigenic determinants of protein HMG-1 are always available to antibody binding in puffed regions, as well as other chromosomal areas.

Localization of chromosomal protein HMG-1 in polytene chromosomes of Chironomus thummi

The distribution of accessible antigenic sites in the chromosomal protein high mobility group one (HMG-1) in Chironomus thummi polytene chromosomes is visualized by immunofluorescence. The results indicate that (a) HMG-1 is distributed in a distinct banding pattern along the entire length of the chromosomes; (b) the banding pattern obtained with fluorescent antibody does not strictly correspond to that observed by phase-contrast microscopy; and (c) the amount of HMG-1 increases, and the fluorescent banding pattern changes, during the development of the organism. Our findings suggest that the protein may be involved in the modulation of the structure of selected loci in the chromosome.

Subcellular compartmentalization of saccharide moieties in cultured normal and malignant cells

We studied subcellular localization of saccharide moieties in cultured normal and malignant cells fixed in paraformaldehyde and treated with a nonionic detergent, using lectins specific for various surgar residues as probes in fluorescence microscopy. In normal cells, concanavalin A and Lens culinaris agglutinin, specific for mannose-rich carbohydrate cores in glycoproteins, labeled the endoplasmic reticulum as a wide perinuclear region. Other lectins, on the other hand, stained the Golgi apparatus as a juxtanuclear reticular structure. A similar compartmentalization was also seen in all malignant cells studied, although the Golgi apparatus in these cells was distinctly vesicular in appearance. Our results indicate that saccharide moieties in both normal and malignant cells are similarly compartmentalized, and thus speak in favor of a unidirectional subcellular flow for both membrane and secreted glycoconjugates.