Transcriptional regulation of the ambient temperature response by h2a.z nucleosomes and hsf1 transcription factors in arabidopsis

Temperature influences the distribution, range, and phenology of plants. The key transcriptional activators of heat shock response in eukaryotes, the heat shock factors (HSFs), have undergone large-scale gene amplification in plants. While HSFs are central in heat stress responses, their role in the response to ambient temperature changes is less well understood. We show here that the warm ambient temperature transcriptome is dependent upon the HSFA1 clade of Arabidopsis HSFs, which cause a rapid and dynamic eviction of H2A.Z nucleosomes at target genes. A transcriptional cascade results in the activation of multiple downstream stress-responsive transcription factors, triggering large-scale changes to the transcriptome in response to elevated temperature. H2A.Z nucleosomes are enriched at temperature-responsive genes at non-inducible temperature, and thus likely confer inducibility of gene expression and higher responsive dynamics. We propose that the antagonistic effects of H2A.Z and HSF1 provide a mechanism to activate gene expression rapidly and precisely in response to temperature, while preventing leaky transcription in the absence of an activation signal.Biological and Soft Matter Physic

Chl4p and Iml3p Are Two New Members of the Budding Yeast Outer Kinetochore

Kinetochore proteins contribute to the fidelity of chromosome transmission by mediating the attachment of a specialized chromosomal region, the centromere, to the mitotic spindle during mitosis. In budding yeast, a subset of kinetochore proteins, referred to as the outer kinetochore, provides a link between centromere DNA-binding proteins of the inner kinetochore and microtubule-binding proteins. Using a combination of chromatin immunoprecipitation, in vivo localization, and protein coimmunoprecipitation, we have established that yeast Chl4p and Iml3p are outer kinetochore proteins that localize to the kinetochore in a Ctf19p-dependent manner. Chl4p interacts with the outer kinetochore proteins Ctf19p and Ctf3p, and Iml3p interacts with Chl4p and Ctf19p. In addition, Chl4p is required for the Ctf19p-Ctf3p and Ctf19p-Iml3p interactions, indicating that Chl4p is an important structural component of the outer kinetochore. These physical interaction dependencies provide insights into the molecular architecture and centromere DNA loading requirements of the outer kinetochore complex

Cnm67p Is a Spacer Protein of the Saccharomyces cerevisiae Spindle Pole Body Outer Plaque

In Saccharomyces cerevisiae, the spindle pole body (SPB) is the functional homolog of the mammalian centrosome, responsible for the organization of the tubulin cytoskeleton. Cytoplasmic (astral) microtubules essential for the proper segregation of the nucleus into the daughter cell are attached at the outer plaque on the SPB cytoplasmic face. Previously, it has been shown that Cnm67p is an integral component of this structure; cells deleted for CNM67 are lacking the SPB outer plaque and thus experience severe nuclear migration defects. With the use of partial deletion mutants of CNM67, we show that the N- and C-terminal domains of the protein are important for nuclear migration. The C terminus, not the N terminus, is essential for Cnm67p localization to the SPB. On the other hand, only the N terminus is subject to protein phosphorylation of a yet unknown function. Electron microscopy of SPB serial thin sections reveals that deletion of the N- or C-terminal domains disturbs outer plaque formation, whereas mutations in the central coiled-coil domain of Cnm67p change the distance between the SPB core and the outer plaque. We conclude that Cnm67p is the protein that connects the outer plaque to the central plaque embedded in the nuclear envelope, adjusting the space between them by the length of its coiled-coil

Supercurrents in Magnesium Diboride/Metal Composite Wire

We have fabricated a series of ex situ copper sheathed powder-in-tube MgB2 wires with 20% by volume Ag, Pb, In, and Ga metal added to the MgB2 powder. We find the transport critical current of these wires increases significantly with the addition of specific metals to the core filament. In particular, the critical current density (Jc) of the MgB2/Ga(20%) wire is in excess of 5x10^4 A/cm^2 at 10K in self field, nearly 50 times that of the MgB2/Ag(20%) wire. The temperature dependent Jc of all wires is well described as an ensemble of clean S/N/S junctions in which the relevant parameters are the average thickness of the N layer, the critical temperature of the S layer, and a scaling term related to Jc at zero temperature. Eliminating the differences in the filament microstructure as the primary cause of the enhanced Jc, we suggest that Jc is determined by the magnitude of the proximity effect induced superconductivity in the normal metal layer, which is known to be proportional to the electron-electron interaction in N. We present one-dimensional material specific calculations that support this, and zero-field cooled DC magnetic susceptibility data that confirm an increased number of well-connected superconducting grains exist in the composite wires that contain metal additions with large electron-electron interactions and long electron mean free paths.Comment: 36 pages, 10 figures, 3 table

Time-Lapse Video Microscopy Analysis Reveals Astral Microtubule Detachment in the Yeast Spindle Pole Mutant cnm67

Saccharomyces cerevisiae cnm67Δ cells lack the spindle pole body (SPB) outer plaque, the main attachment site for astral (cytoplasmic) microtubules, leading to frequent nuclear segregation failure. We monitored dynamics of green fluorescent protein–labeled nuclei and microtubules over several cell cycles. Early nuclear migration steps such as nuclear positioning and spindle orientation were slightly affected, but late phases such as rapid oscillations and insertion of the anaphase nucleus into the bud neck were mostly absent. Analyzes of microtubule dynamics revealed normal behavior of the nuclear spindle but frequent detachment of astral microtubules after SPB separation. Concomitantly, Spc72 protein, the cytoplasmic anchor for the γ-tubulin complex, was partially lost from the SPB region with dynamics similar to those observed for microtubules. We postulate that in cnm67Δ cells Spc72–γ-tubulin complex-capped astral microtubules are released from the half-bridge upon SPB separation but fail to be anchored to the cytoplasmic side of the SPB because of the absence of an outer plaque. However, successful nuclear segregation in cnm67Δ cells can still be achieved by elongation forces of spindles that were correctly oriented before astral microtubule detachment by action of Kip3/Kar3 motors. Interestingly, the first nuclear segregation in newborn diploid cells never fails, even though astral microtubule detachment occurs