Ssn6, a yeast protein that comprises 10 tandem tetratricopeptide repeat (TPR) motifs, associates with Tup1 repressor protein and acts as a transcriptional corepressor. In this report we identify ...point mutations in the TPR1 of Ssn6 that disrupt Tup1 interaction. Furthermore, we construct a 3D model of the TPR domain of Ssn6, which is responsible for Tup1 binding, based on the known structure of protein phosphatase 5. According to this model all selected mutations reduce the ability of Ssn6 to interact with Tup1 by affecting the structural integrity of TPR1 and/or the correct spatial arrangement of TPR1 relative to TPR2 and TPR3.
Since 2014, the University Campus of the Hellenic Open University (HOU) hosts the Astroneu array which is dedicated to the detection of Extensive Air Showers (EAS) induced by high energy Cosmic Rays ...(CR). The Astroneu array incorporates 9 large particle scintillation detectors and 6 antennas sensitive in the Radio Frequency (RF) range 1-200 MHz. The detectors are adjusted in three autonomous stations operating in an environment with strong electromagnetic background. As shown by previous studies, EAS radio detection in such environments is possible using innovative noise rejection methods, as well as advanced analysis techniques. In this work, we present the analysis of the collected radio data corresponding to an operational period of approximately four years. We present the performance of the Astroneu radio array in reconstructing the EAS axis direction using different RF detector geometrical layouts and a technique for the estimation of the shower core by comparing simulation and experimental data. Moreover, we measure the relative amplitudes of the two mechanisms that give rise to RF emission (Askaryan effect and Geomagnetic emission) and show that they are in good agreement with previous studies as well as with the simulation predictions.
The related AP-1 and ATF/CREB families of transcriptional regulatory proteins bind as dimers to overlapping or adjacent DNA half-sites by using a bZIP structural motif. Using genetic selections, we ...isolate derivatives of yeast GCN4 that affect DNA-binding specificity at particular positions of the AP-1 target sequence. In general, altered DNA-binding specificity results from the substitution of larger hydrophobic amino acids for GCN4 residues that contact base pairs. However, in several cases, DNA binding by the mutant proteins cannot be simply explained in terms of the GCN4-AP-1 structure; movement of the protein and/or DNA structural changes are required to accommodate the amino acid substitutions. The quintet of GCN4 residues that make base-pair contacts do not entirely determine DNA-binding specificity because these residues are highly conserved in the bZIP family, yet many of the bZIP proteins bind to distinct DNA sites. The α-helical fork between the GCN4 DNA-binding and dimerization surfaces is important for half-site spacing preferences, because mutations in the fork alter the relative affinity for AP-1 and ATF/CREB sites. The basic region in the protein-DNA complex is a long isolated α-helix, with no constraints from other parts of a folded domain. From all of these considerations, we suggest that small shifts in position and orientation or local deformations in the α-helical backbone distinguish one bZIP complex from another.
The bZIP class of eukaryotic transcriptional regulators utilize a distinct structural motif that consists of a leucine zipper that mediates dimerization and an adjacent basic region that directly ...contacts DNA. Although models of the protein-DNA complex have been proposed, the basis of DNA-binding specificity is essentially unknown. By genetically selecting for derivatives of yeast GCN4 that activate transcription from promoters containing mutant binding sites, we isolate an altered-specificity mutant in which the invariant asparagine in the basic region of bZIP proteins (Asn-235) has been changed to tryptophan. Wild-type GCN4 binds the optimal site (ATGACTCAT) with much higher affinity than the mutant site (TTGACTCAA), whereas the Trp-235 protein binds these sites with similar affinity. Moreover, the Trp-235, Ala-235, and Gln-235 derivatives differ from GCN4 in their strong discrimination against GTGACTCAC. These results suggest a direct interaction between Asn-235 and the ±4 position of the DNA target site and are discussed in terms of the scissors-grip and induced-fork models of bZIP proteins.
The steady-state translational activation of the GCN4 mRNA is based upon an increase in the rate of ribosome initiation at the protein coding AUG following translation of the 5' most proximal open ...reading frame located in its untranslated region. Such an increase is effected when the cellular amount of the GCN2 protein kinase is increased or when the function of the GCD1 gene product is defective. Here, we report conditions that result in a dramatic transient increase in the rate of GCN4 protein synthesis, which also requires the prior translation of the 5' most proximal open reading frame but is independent of the GCN2 protein. This activation of GCN4 mRNA translation coincides with a decrease in the rate of total cellular protein synthesis. We also observed low rates of protein synthesis in the gcd1 strain and in strains that overexpress the GCN2 protein kinase. The process in protein synthesis that is affected is formation of 43S preinitiation complexes. These results reveal the existence of a coupling between this process in translational initiation and the mechanism that activates translation of GCN4 mRNA.
The present paper reports results from a comparative analysis of the effectiveness of regional policy schemes in areas of Scotland and Greece. Discretionary schemes are of a lower gross cost per job ...than automatic ones in both countries. Additionality was found to be very high among all schemes in both countries. Results indicate that future policy design should be decentralised and highly adapted to local condition s. In the case of Greece, the dominant top-bottom style of policy making acts as major constraints in the adoption of more decentralised policy design and delivery mechanisms. In the case of Scotland such a task is easier to accomplish.
The PICOSEC Micromegas precise timing detector is based on a Cherenkov radiator coupled to a semi-transparent photocathode and a Micromegas amplification structure. The first proof of concept ...single-channel small area prototype was able to achieve time resolution below 25 ps. One of the crucial aspects in the development of the precise timing gaseous detectors applicable in high-energy physics experiments is a modular design that enables large area coverage. The first 19-channel multi-pad prototype with an active area of approximately 10 cm\(^2\) suffered from degraded timing resolution due to the non-uniformity of the preamplification gap. A new 100 cm\(^2\) detector module with 100 channels based on a rigid hybrid ceramic/FR4 Micromegas board for improved drift gap uniformity was developed. Initial measurements with 80 GeV/c muons showed improvements in timing response over measured pads and a time resolution below 25 ps. More recent measurements with a new thinner drift gap detector module and newly developed RF pulse amplifiers show that the resolution can be enhanced to a level of 17~ps. This work will present the development of the detector from structural simulations, design, and beam test commissioning with a focus on the timing performance of a thinner drift gap detector module in combination with new electronics using an automated timing scan method.
The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector consisting of a Cherenkov radiator combined with a photocathode and a MM amplifying structure. A 100-channel non-resistive ...PICOSEC MM prototype with 10x10 cm^2 active area equipped with a Cesium Iodide (CsI) photocathode demonstrated a time resolution below 18 ps. The objective of this work is to improve the PICOSEC MM detector robustness aspects; i.e. integration of resistive MM and carbon-based photocathodes; while maintaining good time resolution. The PICOSEC MM prototypes have been tested in laboratory conditions and successfully characterised with 150 GeV/c muon beams at the CERN SPS H4 beam line. The excellent timing performance below 20 ps for an individual pad obtained with the 10x10 cm^2 area resistive PICOSEC MM of 20 MOhm/sq showed no significant time resolution degradation as a result of adding a resistive layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B4C) photocathode presented a time resolution below 35 ps; opening up new possibilities for detectors with robust photocathodes. The results made the concept more suitable for the experiments in need of robust detectors with good time resolution.
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