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81.
Harry Walter Fatima A. Al-Romaihi Eugene J. Krob Geoffrey V. F. Seaman 《Cell biochemistry and biophysics》1987,10(3):217-232
The K-562 cell line is a culture of human leukemia stem cells originally derived from a patient with chronic myelogenous leukemia
in blast crisis. We have subjected such cells, in the log phase of growth, to countercurrent distribution in a charge-sensitive
dextran-polyethylene glycol aqueous-phase system, a method that fractionates cells on the basis of subtle differences in their
surface properties, and found that: (1) The cell population is heterogeneous since it is composed of cells with different
partition ratios. (2) There is a correlation between increasing cell partition ratios and increasing cell electrophoretic
mobilities. (3) Cells under different parts of the distribution curve have dissimilar ratios of cells in different parts of
the cell cycle, a phenomenon that may, at least partially, be the basis for the subfractionation of these cells. There is
a clear tendency for cells in G0+G1+early S to decrease and for those in late S+G2+M to increase with increasing partition ratios. (4) Sialic acid is a major surface charge component of the cells as evidenced
by a dramatic drop in their partition ratios after treatment with neuraminidase. 相似文献
82.
Paired sequence difference in ribosomal RNAs: evolutionary and phylogenetic implications 总被引:12,自引:1,他引:11
Ribosomal RNAs have secondary structures that are maintained by internal
Watson-Crick pairing. Through analysis of chordate, arthropod, and plant 5S
ribosomal RNA sequences, we show that Darwinian selection operates on these
nucleotide sequences to maintain functionally important secondary
structure. Insect phylogenies based on nucleotide positions involved in
pairing and the production of secondary structure are incongruent with
those constructed on the basis of positions that are not. Furthermore,
phylogeny reconstruction using these nonpairing bases is concordant with
other, morphological data.
相似文献
83.
M Barbulescu G Turner M I Seaman A S Deinard K K Kidd J Lenz 《Current biology : CB》1999,9(16):861-868
BACKGROUND: Endogenous retroviruses contribute to the evolution of the host genome and can be associated with disease. Human endogenous retrovirus K (HERV-K) is related to the mouse mammary tumor virus and is present in the genomes of humans, apes and cercopithecoids (Old World monkeys). It is unknown how long ago in primate evolution the full-length HERV-K proviruses that are in the human genome today were formed. RESULTS: Ten full-length HERV-K proviruses were cloned from the human genome. Using provirus-specific probes, eight of the ten were found to be present in a genetically diverse set of humans but not in other extant hominoids. Intact preintegration sites for each of these eight proviruses were present in the apes. A ninth provirus was detected in the human, chimpanzee, bonobo and gorilla genomes, but not in the orang-utan genome. The tenth was found only in humans, chimpanzees and bonobos. Complete sequencing of six of the human-specific proviruses showed that full-length open reading frames for the retroviral protein precursors Gag-Pro-Pol or Env were each present in multiple proviruses. CONCLUSIONS: At least eight full-length HERV-K genomes that are in the human germline today integrated after humans diverged from chimpanzees. All of the viral open reading frames and cis-acting sequences necessary for HERV-K replication must have been intact during the recent time when these proviruses formed. Multiple full-length open reading frames for all HERV-K proteins are present in the human genome today. 相似文献
84.
85.
Patrycja Kozik Richard W. Francis Matthew N. J. Seaman Margaret S. Robinson 《Traffic (Copenhagen, Denmark)》2010,11(6):843-855
Sorting signals for cargo selection into coated vesicles are usually in the form of short linear motifs. Three motifs for clathrin‐mediated endocytosis have been identified: YXXΦ, [D/E]XXXL[L/I] and FXNPXY. To search for new endocytic motifs, we made a library of CD8 chimeras with random sequences in their cytoplasmic tails, and used a novel fluorescence‐activated cell sorting (FACS)‐based assay to select for endocytosed constructs. Out of the five tails that were most efficiently internalized, only one was found to contain a conventional motif. Two contain dileucine‐like sequences that appear to be variations on the [D/E]XXXL[L/I] motif. Another contains a novel internalization signal, YXXXΦN, which is able to function in cells expressing a mutant µ2 that cannot bind YXXΦ, indicating that it is not a variation on the YXXΦ motif. Similar sequences are present in endogenous proteins, including a functional YXXXΦN (in addition to a classical YXXΦ) in cytotoxic T‐lymphocyte‐associated protein 4 (CTLA‐4). Thus, the repertoire of endocytic motifs is more extensive than the three well‐characterized sorting signals. 相似文献
86.
87.
88.
J.P. Famaey J. Fontaine I. Seaman J. Reuse 《Prostaglandins & other lipid mediators》1978,16(5):725-732
Nine non-steroidal antiinflammatory drugs, five steroidal antiinflammatory drugs and four sex steroids were found to potently and reversibly inhibit angiotensin-induced contractions of guinea-pig isolated ileum. The effects of these drugs were reversed by small amounts of PGE1 but the mechanism of their action was probably non selective for angiotensin. 相似文献
89.
Within the tribe Heliantheae of the Asteraceae, the genetic boundaries of the subtribe Melampodinae have recently been drastically revised by Stuessy. The number of genera within the subtribe has been reduced and new generic groupings have been established. The present study correlates the distribution of sesquiterpene lactones found in these genera with the newly revised subtribal boundaries. The genera Acanthospermum, Melampodium, Polymnia and Sigesbeckia produce predominantly melampolide-type sequiterpene lactones. Limited chemical data support Stuessy's removal of the genera Desmanthodium, Clibadium and Ichthyothere from the subtribe Melampodiinae. The occurrence of melampolide-type sesquiterpene lactones in members of the genera Tetragonotheca (Helianthinae) and Enhydra (Ecliptinae) indicate a possible position of these genera in the Melampodiinae. 相似文献
90.
Some physicochemical factors relevant to cellular interactions 总被引:1,自引:0,他引:1
Colloidal stability theory is discussed to accomodate the conditions imposed by biological systems. It is shown that to obtain potential curves with secondary minima, Hamaker's constant must be in the range of 1–5 × 10?14 ergs. The effect of increasing the dielectric constant is shown in theory to lower the surface potential and electrophoretic mobility but to increase the total energy of interaction. Calculations made from the theory predict the forces between model cells to be ca. 4.0 × 10?7 dynes. By cone-plate shearing of cell aggregates, the most successful of several techniques tried and discussed, at shear rates approaching 1 × 10?4 second?1 (1.5 × 10?4 dynes) semi-complete disaggregation was achieved although cell disruption was apparent; analysis of blood viscosity data indicates 5–10 × 10?7 dynes are required to separate red cells suspended in plasma. Colloidal stability theory, while not applicable to cell systems associated by special areas of attachment, seems to describe the physicochemical interaction of freely moving or reversibly adherent cells. 相似文献