Mannosyltransferase activities in membranes from various yeast strains

In the yeast Golgi compartments, at least five, and potentiallyseveral additional mannosyltransferases are involved in elongatingto ‘mannan’ the core Man₈GlcNAc₂ oligosac-charidetrimmed from GlC₃Man₉GlcNAc₂ in the endoplasmic reticulum. Structuralstudies on oligosaccharides from alg3 mutant yeast, which lackthe four upper arm mannoses donated by Man-P-Dol (where Dolis dolichol), verified that the new     

甾体激素受体超家族的基因调控机制

甾体激素受体超家族是一类基因反式作用因子,对RNA聚合酶Ⅱ转录的某些蛋白质基因和RNA聚合酶Ⅰ转录的核糖体RNA基因均有正或负的转录调节作用.超家族对RNA polⅡ转录的基因调控的机理包括受体激活,相关蛋白解离,磷酸化,同源/异源二聚化,核转位,与正/负激素应答元件及相应转录蛋白作用,最终激活或抑制特异靶基因的转录.甾体激素对RNA polⅠ转录的基因的调节作用以及超家族中的经典受体和孤儿受体非配合的激活机制是目前研究的热点.     

Partial characterization of the glucose transport activity in the golgi-rich fraction of fat cells

The glucose transport activity solubilized from the basal and plus insulin forms of the Golgi-rich fraction of adipocytes was partially characterized, and the results were compared with those of the activity obtained from the plus insulin form of the plasma membrane-rich fraction. The transport activity was determined in a cell-free, reconstituted, system. Prior to reconstitution, the activities in the three preparations were all (a) stable at 0°C for at least 4 h, but not at 37°C or above; (b) most stable at pH 7–9, and (c) less stable in Tes than in Tris buffer. After reconstitution, the three activities were all (d) stable at 0°C, (e) most active at pH 5.5, (f) mildly stimulated by divalent cations, (g) unaffected by insulin or 1 mM of several SH-blocking agents, (h) inhibited by heavy metal ions, 10–100 mM of monovalent salts, organic solvents, several sugar isomers, and specific sugar-transport inhibitors. The rates of d-glucose uptake by the three liposome preparations were all inhibited more strongly by 2-deoxy-d-glucose or $\text{3}\text{-O-}\text{methyl-}\text{d}\text{-glucose}$ than by d-glucose. These data indicate that the general properties of the glucose transport activity in the Golgi-rich fraction are similar to those of the activity in the plasma membrane-rich fraction.     

EFFECTS OF HUMAN LEUKOCYTE CONDITIONED MEDIUM ON MOUSE HAEMOPOIETIC PROGENITOR CELLS

Medium conditioned by human peripheral blood leukocytes (HLCM) was studied for its in vitro effects on haemopoietic progenitor cells (CFU-s and CFU-c) present in mouse bone marrow. HLCM has poor colony stimulating activity in semi-solid cultures of mouse bone marrow cells. but invariably increases the number of colonies obtained in the presence of plateau levels of semi-purified colony stimulating factor (CSF). In liquid cultures, HLCM appears to contain a potent initiator of DNA synthesis in CFU-s. an activity which coincides with an increased CFU-s maintenance and causes a three- to four-fold increase in CFU-c number. It is apparent from this study that HLCM, in addition to stimulating colony formation in cultures of human bone marrow cells, has a profound in vitro effect on primitive haemopoietic progenitor cells of the mouse, which cannot be attributed to CSF.     

A new method for the isolation of renal basement membranes

A method is described for the isolation of basement membranes from rabbit renal cortex in which the detergent $\text{N-}\text{lauroyl}$ sarcosine is used as the disruptive agent. The isolated membranes have been compared with membranes prepared using ultrasonication and they were comparable both in terms of purity and gross chemical composition. Glomerular and tubular basement membranes were isolated by first separating glomeruli from tubules by density gradient centrifugation followed by detergent treatment of the separated tissues.The detergent method has the advantage that the basement membranes retained their native structure to a large degree, whereas sonicated membranes were severely fragmented. Collagen fibres were a significant contaminant in both preparations and were revealed more clearly by negative staining than by examination of thin sections. Studies with the detergent-treated membrane revealed that a few proteins, which seemed to be membrane components, were extracted with 1 M NaCl and that these proteins were lost from the basement membranes during sonication used in the conventional isolation procedure.     

Bacterial symbionts on green hydra and their effect on phosphate uptake

Gram-negative rod-shaped bacteria (1.5–2m long and 0.5m wide) have been found associated with green hydra. They are always present on the hydra surface delineating the ectodermal cells, on animals in culture, and also on those sampled from a natural habitat. The bacteria could be removed by a 30-min treatment with antibiotics (50/ml polymyxin B and 50/ml streptomycin). Antibiotic-treated hydra took up 55% less phosphate from the medium than control hydra. The nutritional relationship between the bacteria and green hydra and possible routes of infection of the hydra by these prokaryotic symbionts are discussed. Their importance in interpreting results of certain types of physiological experiments using aquatic organisms is emphasized.     

Cell culture studies on neurofibromatosis (von Recklinghausen)

Summary The growth of strains of fibroblasts derived from patients with neurofibromatosis (NF) was compared with that of strains from appropriate controls in culture medium containing 1% or 15% fetal calf serum. The means of the ratios of final to initial cell numbers do not differ significantly between NF strains and control strains. Weakly significant differences are, however, obtained after conversion of the results to mean numbers of cell population doublings, the NF strains showing the higher numbers. The ratios of final to initial amounts of protein also differ significantly under both sets of growth conditions. High growth parameters occur significantly more frequently among our smaple of 11 NF strains than among our sample of 13 control strains. The possibility of the expression of the NF genotype(s) on the level of the cultured fibroblast-like cells and the possible causes of the large ranges of inter-and intra-individual variations of the results are discussed.     

Analysis of the frequency and distribution of sister chromatid exchanges in cultured human lymphocytes

Summary Lymphocytes from 20 normal subjects (11 male and 9 female) were examined for the frequency and location of sister chromatid exchanges (SCE) by the BrdU—Giemsa method. The mean frequency of SCE was 6.37 with little significant variation. One subject had a high number of exchanges in chromosome 1 while the remainder showed a random distribution of exchanges between chromosomes. The frequency of exchanges generally increased with chromosome length. However, chromosome 1, 2 and the B group had more exchanges than expected while the E, F and G groups had less than expected. The distribution of exchanges in chromosomes 1, 2 and the B group was non-random with a concentration of exchanges below the centromere and to a lesser extent on the distal portion of the long arm. The majority of exchanges appeared to occur at the junction between the dark and light G bands. It is suggested that the concentration of exchanges may reflect differences in BrdU incorporation along the length of the chromosome.     

CULTURE STUDY OF REPRODUCTIVE CYCLES AND SYSTEMATICA IN MOUGEOTIA TRANSEAUI (CHLOROPHYTA)1,2

Asexual and sexual reproductive cyries are described and illustrated for a cultured homothallic strain of Mougeotia transeaui Collins. Reproduction is by aplanospores and zygospores. Aplanospore formation precedes zygospore formation and continues longer with regreening of older cultures occurring regularly from precocious germination of aplanospores. Aplanospores typically form when most of the protoplast moves into the central swollen region of a cell and two new cross walls form to delimit an aplanosporangium. Conjugation is scalariform without the movement and fusion of well-organized gametes. During zygospore maturation, three new cross walls form in the receptive gametangium and conjugation tube to produce a zygosporangium.