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pubmed: 1059-1524



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Constitutive centromere-associated network contacts confer differential stability on CENP-A nucleosomes in vitro and in the cell.
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Constitutive centromere-associated network contacts confer differential stability on CENP-A nucleosomes in vitro and in the cell.

Mol Biol Cell. 2018 Jan 17;:

Authors: Cao S, Zhou K, Zhang Z, Luger K, Straight AF

Abstract
Eukaryotic centromeres are defined by the presence of nucleosomes containing the histone H3 variant, Centromere Protein A (CENP-A). Once incorporated at centromeres, CENP-A nucleosomes are remarkably stable, exhibiting no detectable loss or exchange over many cell cycles. It is currently unclear whether this stability is an intrinsic property of CENP-A containing chromatin or whether it arises from proteins that specifically associate with CENP-A chromatin. Two proteins, CENP-C and CENP-N, are known to bind CENP-A human nucleosomes directly. Here, we test the hypothesis that CENP-C or CENP-N stabilize CENP-A nucleosomes in vitro and in living cells. We show that CENP-N stabilizes CENP-A nucleosomes alone, and additively with CENP-C in vitro However, removal of CENP-C and CENP-N from cells, or mutating CENP-A so that it no longer interacts with CENP-C or CENP-N, had no effect on centromeric CENP-A stability in vivo Thus, the stability of CENP-A nucleosomes in chromatin does not solely arise from its interactions with CENP-C or CENP-N.

PMID: 29343552 [PubMed - as supplied by publisher]




Two subunits of the exocyst, Sec3p and Exo70p, can function exclusively on the plasma membrane.
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Two subunits of the exocyst, Sec3p and Exo70p, can function exclusively on the plasma membrane.

Mol Biol Cell. 2018 Jan 17;:

Authors: Liu D, Li X, Shen D, Novick P

Abstract
The exocyst is an octameric complex that tethers secretory vesicles to the plasma membrane in preparation for fusion. We anchored each subunit with a transmembrane (TM) domain at its N- or C-terminus. Only N-terminally anchored TM-Sec3p and C-terminally anchored Exo70p-TM proved functional. These findings orient the complex with respect to the membrane and establish that Sec3p and Exo70p can function exclusively on the membrane. The functions of TM-Sec3p and Exo70p-TM were largely unaffected by blocks in endocytic recycling suggesting that they act on the plasma membrane, rather than on secretory vesicles. Cytosolic pools of the other exocyst subunits were unaffected in TM-sec3 cells, while they were partially depleted in exo70-TM cells. Blocking actin-dependent delivery of secretory vesicles in act1-3 cells results in loss of Sec3p from the purified complex. Our results are consistent with a model in which Sec3p and Exo70p can function exclusively on the plasma membrane while the other subunits are brought to them on secretory vesicles.

PMID: 29343551 [PubMed - as supplied by publisher]




Cdk1-dependent phospho-inhibition of a formin-F-BAR interaction opposes cytokinetic contractile ring formation.
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Cdk1-dependent phospho-inhibition of a formin-F-BAR interaction opposes cytokinetic contractile ring formation.

Mol Biol Cell. 2018 Jan 17;:

Authors: Willet AH, Bohnert KA, Gould KL

Abstract
In Schizosaccharomyces pombe, cytokinesis requires the assembly and constriction of an actomyosin-based contractile ring (CR). A single essential formin, Cdc12, localizes to the cell middle upon mitotic onset and nucleates the F-actin of the CR. Cdc12 medial recruitment is mediated in part by its direct binding to the F-BAR scaffold Cdc15. Given that Cdc12 is hyper-phosphorylated in M phase, we explored whether Cdc12 phospho-regulation impacts its association with Cdc15 during mitosis. We found that Cdk1, a major mitotic kinase, phosphorylates Cdc12 on six N-terminal residues near the Cdc15-binding site. Cdc12 phosphorylation of Cdc12 on these sites inhibits its interaction with the Cdc15 F-BAR domain. Consistent with this finding, a cdc12 mutant with all six Cdk1 sites changed to phospho-mimetic residues (cdc12-6D) displays similar phenotypes to cdc12-P31A, in which the Cdc15-binding motif is disrupted; both show reduced Cdc12 at the CR and delayed CR formation. Together, these results indicate that Cdk1 phosphorylation of formin Cdc12 antagonizes its interaction with Cdc15 and thereby opposes Cdc12's CR localization. These results are consistent with a general role for Cdk1 in inhibiting cytokinesis until chromosome segregation is complete.

PMID: 29343550 [PubMed - as supplied by publisher]




Intracellular vesicle trafficking plays an essential role in mitochondrial quality control.
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Intracellular vesicle trafficking plays an essential role in mitochondrial quality control.

Mol Biol Cell. 2018 Jan 17;:

Authors: Gerards M, Cannino G, de Cózar JMG, Jacobs HT

Abstract
The Drosophila gene products Bet1, Slh and CG10144, predicted to function in intracellular vesicle trafficking, were previously found to be essential for mitochondrial nucleoid maintenance. Here we show that Slh and Bet1 co-operate to maintain mitochondrial functions. In their absence, mitochondrial content, membrane potential and respiration became abnormal, accompanied by mitochondrial proteotoxic stress, but without direct effects on mtDNA. Immunocytochemistry showed that both Slh and Bet1 are localized at the Golgi, together with a proportion of Rab5-positive vesicles. Some Bet1, as well as a tiny amount of Slh, co-fractionated with highly purified mitochondria, whilst live-cell imaging showed coincidence of fluorescently tagged Bet1 with most Lysotracker-positive and a small proportion of Mitotracker-positive structures. This 3-way association was disrupted in cells knocked down for Slh, although co-localized lysosomal and mitochondrial signals were still seen. Neither Slh nor Bet1 were required for global mitophagy or endocytosis, but prolonged Slh knockdown resulted in G2 growth arrest, with increased cell diameter. These effects were shared with knockdown of betaCOP but not of CG1044, Snap24 or Syntaxin6. Our findings implicate vesicle sorting at the cis-Golgi in mitochondrial quality control.

PMID: 29343549 [PubMed - as supplied by publisher]