Indirect DNA Readout by an H-NS Related Protein: Structure of the DNA Complex of the C-Terminal Domain of Ler

Ler, a member of the H-NS protein family, is the master regulator of the LEE pathogenicity island in virulent Escherichia coli strains. Here, we determined the structure of a complex between the DNA-binding domain of Ler (CT-Ler) and a 15-mer DNA duplex. CT-Ler recognizes a preexisting structural pattern in the DNA minor groove formed by two consecutive regions which are narrower and wider, respectively, compared with standard B-DNA. The compressed region, associated with an AT-tract, is sensed by the side chain of Arg90, whose mutation abolishes the capacity of Ler to bind DNA. The expanded groove allows the approach of the loop in which Arg90 is located. This is the first report of an experimental structure of a DNA complex that includes a protein belonging to the H-NS family. The indirect readout mechanism not only explains the capacity of H-NS and other H-NS family members to modulate the expression of a large number of genes but also the origin of the specificity displayed by Ler. Our results point to a general mechanism by which horizontally acquired genes may be specifically recognized by members of the H-NS family

STGC ASSEMBLING AND TESTING IN CHILE FOR THE ATLAS MUON SPECTROMETER

The forthcoming luminosity upgrade of LHC will increase the expected background rate in the forward region of the ATLAS Muon Spectrometer. The most important upgrade project for the ATLAS is the replacement of the present Small Wheel by the so-called New Small Wheel (NSW). The NSW will be installed during the LHC long shutdown in 2019/2020. A small-strip Thin Gap Chamber (sTGC) was developed to provide fast trigger and high precision muon tracking under high luminosity LHC condition. Construction of sTGC modules is performed by five countries: Canada, Chile, China, Israel, and Russia. Construction of sTGC wedges is performed at CERN in a collaborative effort. Production in Chile is presented here including testing results as well as first wedge construction

Small-Strip Thin Gap Chambers for the Muon Spectrometer Upgrade of the ATLAS Experiment

The instantaneous luminosity of the Large Hadron Collider at CERN will be increased up to a factor of five with respect to the design value by undergoing an extensive upgrade program over the coming decade. Such increase will allow for precise measurements of Higgs boson properties and extend the search for new physics phenomena beyond the Standard Model. The largest phase-1 upgrade project for the ATLAS Muon System is the replacement of the present first station in the forward regions with the so-called New Small Wheels (NSWs) during the long-LHC shutdown in 2019/20. Along with Micromegas, the NSWs will be equipped with eight layers of small-strip thin gap chambers (sTGC) arranged in multilayers of two quadruplets, for a total active surface of more than 2500 m$^2$. All quadruplets have trapezoidal shapes with surface areas up to 2 m$^2$. To retain the good precision tracking and trigger capabilities in the high background environment of the high luminosity LHC, each sTGC plane must achieve a spatial resolution better than 100 μm to allow the Level-1 trigger track segments to be reconstructed with an angular resolution of approximately 1mrad. The basic sTGC structure consists of a grid of gold-plated tungsten wires sandwiched between two resistive cathode planes at a small distance from the wire plane. The precision cathode plane has strips with a 3.2mm pitch for precision readout and the cathode plane on the other side has pads for triggering. The position of each strip must be known with an accuracy of 30 µm along the precision coordinate and 80 µm along the beam. The mechanical precision is a key point and must be controlled and monitored all along the process of construction and integration. The sTGC detectors are currently being produced and tested in five countries and assembled into wedges at CERN for integration into ATLAS. The sTGC design, performance, construction and integration status will be discussed, along with results from tests of the chambers with nearly final electronics with beams and cosmic rays

Status of the MDT Trigger Processor for the ATLAS Level-0 Muon Trigger at the HL-LHC

The MDT Trigger Processor (MDTTP) is a key ATLAS Level-0 Muon trigger upgrade component designed to meet High-Luminosity LHC requirements. The MDTTP will use MDT hits in the trigger for the first in ATLAS to improve the momentum resolution of muon candidates provided by RPC and TGC detectors and reduce fake muon trigger rate. The MDTTP hardware is based on the Apollo ATCA platform. The pre-production prototype includes a VU13P-FPGA, high-speed FireFly optical transceivers, peripherals, and other improvements learned from using the previous hardware demonstrator. We present the prototype status, firmware implementation, core algorithm, slow-control software, and first integration tests

Status of the MDT Trigger Processor for the ATLAS Level-0 Muon Trigger at the HL-LHC

The MDT Trigger Processor (MDTTP) is a key ATLAS Level-0 Muon trigger upgrade component designed to meet High-Luminosity LHC requirements. The MDTTP will use MDT hits in the hardware level trigger for the first time in ATLAS to improve the momentum resolution of muon candidates provided by RPC and TGC detectors and reduce the fake muon trigger rate. The MDTTP hardware is based on the Apollo ATCA platform. The prototype includes a VU13P-FPGA, high-speed FireFly optical transceivers, peripherals, and other improvements learned from using the previous hardware demonstrator. We present the prototype status, firmware implementation, core algorithm, slow-control software, and first integration tests

Bacterial-Chromatin Structural Proteins Regulate the Bimodal Expression of the Locus of Enterocyte Effacement (LEE) Pathogenicity Island in Enteropathogenic Escherichia coli

In enteropathogenic Escherichia coli (EPEC), the locus of enterocyte effacement (LEE) encodes a type 3 secretion system (T3SS) essential for pathogenesis. This pathogenicity island comprises five major operons (LEE1 to LEE5), with the LEE5 operon encoding T3SS effectors involved in the intimate adherence of bacteria to enterocytes. The first operon, LEE1, encodes Ler (LEE-encoded regulator), an H-NS (nucleoid structuring protein) paralog that alleviates the LEE H-NS silencing. We observed that the LEE5 and LEE1 promoters present a bimodal expression pattern, depending on environmental stimuli. One key regulator of bimodal LEE1 and LEE5 expression is ler expression, which fluctuates in response to different growth conditions. Under conditions in vitro considered to be equivalent to nonoptimal conditions for virulence, the opposing regulatory effects of H-NS and Ler can lead to the emergence of two bacterial subpopulations. H-NS and Ler share nucleation binding sites in the LEE5 promoter region, but H-NS binding results in local DNA structural modifications distinct from those generated through Ler binding, at least in vitro. Thus, we show how two nucleoid-binding proteins can contribute to the epigenetic regulation of bacterial virulence and lead to opposing bacterial fates. This finding implicates for the first time bacterial-chromatin structural proteins in the bimodal regulation of gene expression

Measurement of the intrinsic hadronic contamination in the NA64<math altimg="si2.svg" display="inline" id="d1e670"><mrow><mo>−</mo><mi>e</mi></mrow></math> high-purity <math altimg="si3.svg" display="inline" id="d1e678"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>/</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> beam at CERN

We present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c. The analysis, performed using data collected by the NA64-e experiment in 2022, is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64 detector. We determined the contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those from a dedicated setup, in which only hadrons impinged on the detector. We also obtained an estimate of the relative protons, anti-protons and pions yield by exploiting the different absorption probabilities of these particles in matter. We cross-checked our results with a dedicated Monte Carlo simulation for the hadron production at the primary T2 target, finding a good agreement with the experimental measurements