Asparagine-linked sugar chains of glycoproteins can be classified structurally into three groups; the high mannose type, the complex type and the hybrid type. The occurrence of common core structure in each group is accounted for by the unique biosynthetic pathway of the asparaginelinked sugar chains. Accumulating evidence showing that the outer chain moieties of the complex type sugar chains have structural variations suggests that they play key roles in cellular recognition processes.

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Nuceloli were isolated from the cellular slime mold, Dictyostelium discoideum, strain A-3 without treating the cells with detergent. Electron microscopy showed that the nucleoli were clean and free of contamination by other subcellular organelles. The nucleoli were not surrounded with nucleolus-associated chromatin, but were tightly attached to the nuclear envelopes. The nucleoli contained very little DNA (1.2 %), but contained considerable RNA (16.3 %). Analysis of the protein components on a SDS-polyacrylamide gel showed many protein bands in a range of molecular weight between. 10, 000 and 50, 000 daltons that are related to ribosomal proteins in the cytoplasm. The phosphorylation profile in vitro indicated that most of the nucleolar proteins were labeled to some extent with [³²P]. [5-³H]UTP incorporation into the nucleoli in vitro was inhibited by actinomycin D, but was completely insensitive to α-amanitin; thus, the isolated nucleoli were morphologically intact, and were engaged in ribosomal RNA synthesis.

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Transport of α-aminoisobutyric acid (AIB) by membrane vesicles from virally transformed and nontransformed cells was analyzed under various assay conditions. Trypsin treatment or the addition of 100 mM NaSCN for driving force resulted in the generation of a transient concentrative uptake of AIB (overshoot) by nontransformed cell membranes, although the shape of the overshoot differed from that of transformed cell membranes in the same conditions of transport assay. Thus, the overshoot is not a specific phenomenon for transformed cell membranes. Furthermore, at the low temperature (5°) of assay incubation, the pattern of AIB transport by transformed cell membranes resembled that by nontransformed cell membranes in the slow initial rate of uptake and prolonged overshoot. Therefore, in the mechanism. for AIB transport, there may be no fundamental differences between transformed and nontransformed cell membranes.

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Using low temperature and colchicine, we examined how axopodia play a role in the initiation and subsequent process of cell fusion in a large heliozoan Echinosphaerium nucleofilum (strain MA). Although the fusion reaction is naturally temperature-dependent, preliminary treatment with a low temperature (2°C) induced the reaction more efficiently than in the control kept at room temperature (20°C). During the recovery process from the cold, the reaction was enhanced conspicuously in the presence of colchicine; the fusion indices were 2.05 to 5.68 after a 9 h incubation with 4 to 8 mM colchicine. When treated with 4 to 10 mM colchicine without the preliminary cold treatment, the reaction also was enhanced. This means that the reaction depended upon the colchicine concentration and resulted in partial or complete degradation of axopodia; fusion indices were 1.08 to 3.77 after a 9 h incubation with 4 to 10 mM colchicine. We discuss these results and the electron-microscopical data, in relation to the role of axopodia in the fusion reaction.

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To prepare an oversized and synchronized cell sample, exponentially growing cells of Schizosaccharomyces pombe were exposed to 8 mM hydroxyurea for 3 h, then transferred to a poor medium (0.5 % malt medium or nitrogen-free minimal medium). The transferred cells were grown in a small chamber without shaking and observed by time-lapse photomicrography. Cells cultivated in the poor medium divided twice synchronously, but hardly elongated in cell length between the two divisions. Under this condition, the relationship between cell size and cycle duration (the time interval between the divisions) was investigated. Cells smaller than a particular size had a negative correlation between cell size at birth and cycle duration. Cells above the particular cell size had a constant minimum cycle duration. Cells divided regardless of size at division. These results suggest that cycle duration depends on cell size at birth, not at division.

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Nuclear acidic proteins solubilized from young and senescent human diploid fibroblasts were analyzed by two-dimensional gel electrophoresis. The age-related increase in nuclear proteins was due mainly to the accumulation of residual acidic proteins. Differences in seven major nuclear acidic proteins between young and senescent cells were observed. [³⁵S]-menthionine autoradiography showed that senescent cells had lost the ability to synthesize detectable amounts of four major proteins that are found in young cells. In addition, senescent cells synthesized two new major proteins that were undetectable in young cells. The isoelectric point of a single polypeptide with the molecular weight 37, 000 seemed to shift from 5.3 to 5.8 with cellular aging.

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The attachment of concanavalin A (Con A) to the cell surface of mammary tumor cells reduced the electrophoretic mobility of the cells at ionic strengths higher than 0.1, but not at strengths lower than 0.03. On chondroitinase-ABC treatment, no further reduction in mobility was observed in the cells treated with Con A at ionic strengths higher than 0.1. However, at strengths lower than 0.03, further reduction in mobility was observed that was as great as that observed with intact cells. In the Con A-treated cells, the amount of chondroitin sulfate removed from the cell surface by the enzyme digestion was larger than that removed from the intact cell surface in spite of the unchanged mobility on electrophoresis. The Con A effect on the distribution of the acidic surface sugars was prevented by a pretreatment with 10^-5M N-ethylenmaleimide, a SH-blocking reagent.
The results indicate that the binding of Con A to the cell surface may cause translocation of chondroitin sulfate from the peripheral zone at 0-10Å to a deeper zone at 17-24Å.

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The effect of neocarzinostatin (NCS) on the cell cycle traverse of BHK cells was examined with flow microfluorometry and [³H]-thymidine incorporation. At a low concentration (1μg/ml) of NCS a large number of cells were arrested at the G₂ phase. At a high concentration (10μg/ml) cell cycle traverse from the G₁ to the S phase and DNA synthesis in the middle S phase were inhibited.
Chain elongation, strand scission and repair of DNA were determined by alkaline sedimentation analysis. In the presence of 10μg/ml NCS, parental DNA was degraded to the size of the replication unit (1.1×10⁸dalton). DNA elongated at most to the size of the replication unit, before the parental DNA was degraded to the same size. DNA strand scission took place even at the low concentration of NCS that induced G₂ arrest. The DNA strand scission induced by 10μg/ml NCS was repaired only slightly by 5 h afer the removal of NCS.
A short exposure of cells to NCS was sufficient to cause the inhibition of DNA synthesis and cell cycle traverse, as well as DNA strand scission.

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Cultured HeLa cells were treated with chemicals that affect or bind to the cell membrane (ouabain, amphotericin B and Concanavalin A) or with chemicals related to the membrane function (cyclic nucleotides).Divisions in treated cells were subsequently observed in the living state. Ouabain, at concentrations greater than 10^-8M, significantly prolonged metaphase in treated cells. Excess potassium partially reversed the metaphaseprolonging effect of 10^-7M ouabain but little affected the prolongation caused by 10^-6M. Amphotericin B, at 10 μg per ml, also prolonged metaphase. Concanavalin A (Con A), up to 100 μg per ml, did not affect significantly mitosis. One mM N⁶, 0²'-dibutyryl adenosine-3', 5'-cyclic monophosphate (DBcAMP) did not affect mitosis in treated cells but arrested cells in the G₂ phase of the cell cycle. In the presence of theophylline 1 mM DBcAMP caused a slight but significant prolongation of metaphase, but theophylline alone effected this prolongation to the same degree. In contrast, 1 mM N⁶, 0²'dibutyryl guanosine-3', 5'-monophosphate (DBcGMP), with or without added theophylline, significantly prolonged metaphase.

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Changes in fluorescence intensity of a thiocarbocyanine dye (diS-C₃-(5)) were monitored in rat peritoneal mast cells in the presence of histamine releasers. Compound 48/80, a specific histamine releaser, increased fluorescence intensity which reached a maximum in 3-4 min ; thereafter it gradually returned to a steady state. These changes in the fluorescence intensity were dependent upon the ionic environment and the energy state of the mast cells. By contrast, histamine release from mast cells induced by comp. 48/80 was completed within 10 sec. These data indicate that the comp. 48/80-induced histamine release is not directly associated with the change in membrane potential except at the onset.

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The mitotic behaviour of spheroplasts prepared from synchronized cells of Saccharomyces cerevisiae IFO 0971 in a liquid medium varied with cell density. When incubated at low cell density, spheroplasts entered the first round of mitosis in partial synchrony and most proceeded to the second round. When incubated at high cell density, they showed significant retardation of mitosis, although they apparently carried out one normal round of DNA synthesis. These and other observations indicate that in spheroplast cells incubated at high cell density, some biochemical reactions necessary for the initiation of mitosis are retarded. An additional observation suggested that spheroplast cells may undergo normal mitosis only in the presence of relatively high concentrations of nutrients in the surrounding medium.

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