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At least 235 records · Page 13Linked to original sources
PubMed1998

Nuclear envelope and nuclear pore assembly: analysis of assembly intermediates by electron microscopy.

At mitosis, the nucleus of higher eukaryotic cells disassemblies into components which subsequently reform functional nuclear envelopes in the two daughter cells. The molecular mechanisms underlying this remarkable morphological reorganization are the focus of active investigation. Recent electron microscopy techniques have provided intriguing glimpses of intermediate structures in both nuclear envelope and nuclear pore complex reassembly.

Animals↗
PubMed1998

Role of the yeast Gin4p protein kinase in septin assembly and the relationship between septin assembly and septin function.

To identify septin-interacting proteins in Saccharomyces cerevisiae, we screened for mutations that are synthetically lethal with a cdc12 septin mutation. One of the genes identified was GIN4, which encodes a protein kinase related to Hsl1p/Nik1p and Ycl024Wp in S. cerevisiae and to Nim1p/Cdr1p and Cdr2p in Schizosaccharomyces pombe. The Gin4p kinase domain displayed a two-hybrid interaction with the COOH-terminal portion of the Cdc3p septin, and Gin4p colocalized with the septins at the mother-bud neck. This localization depended on the septins and on the COOH-terminal (nonkinase) region of Gin4p, and overproduction of this COOH-terminal region led to a loss of septin organization and associated morphogenetic defects. We detected no effect of deleting YCL024W, either alone or in combination with deletion of GIN4. Deletion of GIN4 was not lethal but led to a striking reorganization of the septins accompanied by morphogenetic abnormalities and a defect in cell separation; however, remarkably, cytokinesis appeared to occur efficiently. Two other proteins that localize to the neck in a septin-dependent manner showed similar reorganizations and also appeared to remain largely functional. The septin organization observed in gin4Delta vegetative cells resembles that seen normally in cells responding to mating pheromone, and no Gin4p was detected in association with the septins in such cells. The organization of the septins observed in gin4Delta cells and in cells responding to pheromone appears to support some aspects of the model for septin organization suggested previously by Field et al. (Field, C.M., O. Al-Awar, J. Rosenblatt, M.L. Wong, B. Alberts, and T.J. Mitchison. 1996. J. Cell Biol. 133:605-616).

Amino Acid Sequence↗
PubMed1980

Membrane assembly in retinal photoreceptors I. Freeze-fracture analysis of cytoplasmic vesicles in relationship to disc assembly.

To study precursor-product relationships between cytoplasmic membranes of the inner segment of photoreceptors and the continually renewed outer disc membrane, we have compared the density and size distribution of intramembrane particles (IMP) in various membrane compartments of freeze-fractured photoreceptor inner and outer segments. Both rod and cone outer segments of Xenopus laevis are characterized by a relatively uniform distribution of approximately 4,400-4,700 IMP/micron2 in P-face (PF) leaflets of disc membranes. A similar distribution of IMP is found in the outer segment plasma membrane, the ciliary plasma membrane, and in the plasma membrane of the inner segment in the immediate periciliary region. In each case the size distribution of IMP can be characterized as unimodal with a mean diameter of approximately 10 nm. PF leaflets of endoplasmic reticulum, Golgi complex, and vesicles near the cilium have IMP with a size distribution like that in the cilium and outer segment, but with an average density of approximately 2,000/micron2. In contrast, IMP are smaller in average size (approximately 7.5 nm) in PF leaflets of inner segment plasma membrane, exclusive of the periciliary rgion. The similarity of size distribution of IMP in inner segment cytoplasmic membranes and those within the plasmalemma of the cilium and outer segment suggest a precursor-product relationship between the two systems. The structure of the vesicle-rich periciliary region and the segregation of IMP with different size distributions in this region suggest that components destined for incorporation into the outer segment exist as preformed membrane packages (vesicles) which fuse with the inner segment plasma membrane in the periciliary region. Subsequently, membrane components may be transferred to forming discs of the outer segment via the ciliary plasma membrane.

Animals↗
PubMed1988

In vitro hexagonal assembly of R-form lipopolysaccharides: effect of pH on the Mg+2-mediated hexagonal assembly.

The R-form lipopolysaccharide (LPS) from Escherichia coli K-12, from which cationic material had been removed by electrodialysis and the pH of which had fallen to 3.6, formed a rough hexagonal lattice structure with the lattice constant of about 19 nm. The rough hexagonal structure was maintained in buffers at pH 5 or lower but disintegrated into the ribbon-like structures in buffers at pH 6 or higher. However, in the presence of 10 mM Mg2+, the hexagonal lattice structure was not disintegrated even at alkaline pH levels but conversely it became more dense. At pH 8.3 to 8.9, the hexagonal lattice structure with the shortest lattice constant (15 nm) was formed. The same optimal pH levels were obtained for formation of the dense hexagonal lattice structure (lattice constant, 14 to 15 nm) by the electrodialyzed LPS from Klebsiella pneumoniae strain LEN-111 (O3-:K1-). The ability of Mg2+ to induce formation of the dense hexagonal lattice structure of the K-12 LPS depends upon the presence of buffers showing the optimal pH levels, since a very high concentration of Mg2+ such as 500 mM was required for the lattice formation in distilled water. The amount of the magnesium bound to the K-12 LPS did not significantly differ throughout the pH range of 3 to 9. Therefore, the optimal pH range is another essential factor for formation of the dense hexagonal lattice structure of the LPS in addition to binding of the magnesium to the LPS.

Dialysis↗