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21.
Changes in chromatin structure during the mitotic cycle 总被引:3,自引:0,他引:3
P. W. Barlow 《Protoplasma》1977,91(2):207-211
Summary Optical density profiles of Feulgen-stained nuclei ofBryonia dioica at different stages of the mitotic cycle were determined. Nuclei in the G2 phase have a greater fraction of dense chromatin than nuclei in G1 phase. However, nuclei at the end of the S phase have dispersed chromatin of minimal density. Thus, chromatin density oscillates during the mitotic cycle of this species, consequently the progressive increase in density previously recorded throughout the intermitotic period of two other species (onion and mouse) cannot be a general rule. 相似文献
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24.
In vitro fertilization, development, and implantation after exposure of mature mouse oocytes to visible light. 总被引:1,自引:0,他引:1
P Barlow F Puissant P Van der Zwalmen J Vandromme P Trigaux F Leroy 《Molecular reproduction and development》1992,33(3):297-302
Mature mouse oocytes were exposed prior to in vitro fertilization to visible light during 1, 2, or 4 hr at an intensity of 4,000 lux. Compared to controls cultured under identical conditions but protected from light, exposed eggs did not show any significant modification of cleavage speed and rate. After transfer of blastocysts obtained in vitro in uteri of pseudopregnant females, the implantation rate and the proportion of normal fetuses were not found to be different in relation to preliminary light exposure of oocytes fertilized and cultured in vitro. 相似文献
25.
Computer-aided molecular modelling of the endothelin (ET-A) receptor antagonists, BQ-123 and BE-18257B, shows that they have very similar 3D structures. Parts of their 3D structures are also shown to match closely with that reported for residues 6-8 in endothelin-1. On the basis of these similarities (and with supporting evidence from literature data on endothelin structure-activity relationships) a structural determinant is proposed for ET-A receptor binding, and novel designs of peptide are suggested for providing more potent and selective ET-A receptor antagonists. 相似文献
26.
Mitosis in Mantoniella squamata (Manton and Parke) Desikachary, a small scale-covered green monad, is presented. Organelle replication precedes nuclear division and begins with the replication of the chloroplast. As the chloroplasts separate, the Golgi and flagellar apparatuses divide. The discoid microbody enlarges and becomes ‘V'-shaped, with the arms extending toward depressions in the pyrenoid stalks of the chloroplasts. At prophase, microtubules produced by an amorphous microtubule organizing center enter the nucleus via polar fenestre. The nuclear membrane remains intact. As the chloroplasts migrate further apart, the spindle pole-to-pole distance increases. By metaphase, daughter-cell lobes are discernible as a cleavage furrow, which appears as early as prophase, and begins to incise the cell. A single Golgi apparatus is situated near the spindle pole; the flagellar apparatus lies adjacent to the pole. The cleavage furrow continues to constrict the cell, resulting in a narrowing isthmus containing the elongate microbody, nucleus and a rootlet system connecting the basal bodies of the daughter flagella. At telophase, no extra-nuclear microtubular systems other than the previously observed rootlet are present and the nuclei remain separated from each other. In cells undergoing multiple divisions to produce more than two daughter cells, the orientation of organelles changes somewhat, with the basal bodies and the Golgi apparatus separating daughter nuclei prior to the onset of cytokinesis. The mechanics of mitosis in Mantoniella are compared with other green monads and the evolutionary implications discussed. 相似文献
27.
R.G. Barlow 《Journal of experimental marine biology and ecology》1982,63(3):209-227
Investigations on phytoplankton communities in a nearshore region off the Cape Peninsula revealed three types of upwelled water. During active upwelling temperatures were < 10 °C and concentrations of inorganic nutrients were high (Type 1). Maturing upwelled water was characterized by temperatures > 10°C and nitrate concentrations varying between 2 and 15 μg-at. NO3-N · 1?1 (Type 2), while aged upwelled water (Type 3) contained low concentrations of nitrate (<2 μg-at. NO3-N · 1?1) at temperatures > 10°C. During the summer of 1978–1979 diatoms dominated the communities from October to January but microflagellates were dominant in February and March. In both types of community, low concentrations of ATP, chlorophyll a, protein and carbohydrate were measured in Type 1 water with protein/carbohydrate ratios being > 1. In Type 2 water concentrations of chlorophyll a, ATP and protein were high and the protein/carbohydrate ratio was > 1. Concentrations of chlorophyll a and ATP remained high in Type 3 water but the protein/carbohydrate ratio decreased to < 1 due to an increase in the concentration of acid-soluble glucan. It was concluded that the communities were in an active phase of growth in Type 1 and Type 2 water when adequate nutrients were available, but were in a slow-growing phase in Type 3 water when nitrate concentrations were low. Correlation coefficients, simple linear regressions and stepwise multiple regressions between biochemical and environmental variables confirmed that nitrate was the nutrient most closely related to the biochemical composition of phytoplankton. Using linear regression equations of biochemical variables on glucan it was estimated that chlorophyll a existed in a ratio of ≈ 1: 1 between living phytoplankton and bacteria/detritus, while the percentage of ATP was high in the phytoplankton component of Type 1 water but low in that of Type 2 water. The percentage of protein in detritus was greater than in living phytoplankton, and the carbohydrate content of living phytoplankton increased as the upwelled water matured from Type 1 and Type 2 to Type 3. 相似文献
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29.
Thymidine and uridine transporters in peripheral pig lymphocytes have structural features in common, but are not identical. Accelerated entry of [3H]thymidine begins 12h after the addition of phytohaemagglutinin. The increased thymidine uptake into the cells is characterized by an increase in Vmax. Without alteration of the apparent Km(0.6+/-0.08muM). Thymidine kinase activity is increased 12h after stimulation. Both the increased thymidine uptake and the increased thymidine kinase activity are inhibited in cultures incubated with puromycin: rates of degradation of the two systems are unchanged after phytohaemagglutinin addition, and indicate similar half-lives of about 2h. Thymidine kinase is rate-limiting for thymidine entry up to 18h after phytohaemagglutinin addition; increase in its synthesis is detectable about 6h before net incorporation of thymidine into DNA is significantly promoted. 相似文献
30.
Dinesh C. Soares Paul N. Barlow David J. Porteous Rebecca S. Devon 《Journal of molecular modeling》2009,15(2):113-122
Defects in the human ALS2 gene, which encodes the 1,657-amino-acid residue protein alsin, are linked to several related motor neuron diseases. We created
a structural model for the N-terminal 690-residue region of alsin through comparative modelling based on regulator of chromosome
condensation 1 (RCC1). We propose that this alsin region contains seven RCC1-like repeats in a seven-bladed beta-propeller
structure. The propeller is formed by a double clasp arrangement containing two segments (residues 1–218 and residues 525–690).
The 306-residue insert region, predicted to lie within blade 5 and to be largely disordered, is poorly conserved across species.
Surface patches of evolutionary conservation probably indicate locations of binding sites. Both disease-causing missense mutations—Cys157Tyr
and Gly540Glu—are buried in the propeller and likely to be structurally disruptive. This study aids design of experimental
studies by highlighting the importance of construct length, will enhance interpretation of protein–protein interactions, and
enable rational site-directed mutagenesis.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献