ALBERT

Description: The chromatin-remodelling complex B-WICH, comprised of William syndrome transcription factor, the ATPase SNF2h and nuclear myosin, specifically activates RNA polymerase III transcription of the 5S rRNA and 7SL genes. However, the underlying mechanism is unknown. Using high-resolution MN walking we demonstrate here that B-WICH changes the chromatin structure in the vicinity of the 5S rRNA and 7SL RNA genes during RNA polymerase III transcription. The action of B-WICH is required for the binding of the RNA polymerase machinery and the regulatory factors c-Myc at the 5S rRNA and 7SL RNA genes. In addition to the c-Myc binding site at the 5S genes, we have revealed a novel c-Myc and Max binding site in the intergenic spacer of the 5S rDNA. This region also contains a region remodelled by B-WICH. We demonstrate that c-Myc binds to both sites in a Max-dependent way, and thereby activate transcription by acetylating histone H3. The novel binding patterns of c-Myc and Max link transcription of 5S rRNA to the Myc/Max/Mxd network. Since B-WICH acts prior to c-Myc and other factors, we propose a model in which the B-WICH complex is required to maintain an open chromatin structure at these RNA polymerase III genes. This is a prerequisite for the binding of additional regulatory factors.

Description: We present an overview of and first results from the OMEGA (OSIRIS Mapping of Emission-line Galaxies in the multicluster system A901/2) survey. The ultimate goal of this project is to study star formation and active galactic nucleus (AGN) activity across a broad range of environments at a single redshift. Using the tuneable-filter mode of the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) instrument on Gran Telescopio Canarias, we target H α and $[\mathrm{N}\,\small {II}]$ emission lines over an ~0.5 0.5 deg 2 region containing the z  ~ 0.167 multicluster system A901/2. In this paper, we describe the design of the survey, the observations and the data analysis techniques developed. We then present early results from two OSIRIS pointings centred on the cores of the A901a and A902 clusters. AGN and star-forming (SF) objects are identified using the $[\mathrm{N}\,\small {II}]\,/\,\mathrm{H}\,\alpha$ versus W H α diagnostic diagram. The AGN hosts are brighter, more massive, and possess earlier type morphologies than SF galaxies. Both populations tend to be located towards the outskirts of the high-density regions we study. The typical H α luminosity of these sources is significantly lower than that of field galaxies at similar redshifts, but greater than that found for A1689, a rich cluster at z  ~ 0.2. The H α luminosities of our objects translate into star formation rates (SFRs) between ~0.02 and 6 M yr –1 . Comparing the relationship between stellar mass and H α-derived SFR with that found in the field indicates a suppression of star formation in the cores of the clusters. These findings agree with previous investigations of this multicluster structure, based on other star formation indicators, and demonstrate the power of tuneable filters for this kind of study.

Description: Alternative polyadenylation increases transcriptome diversity by generating multiple transcript isoforms from a single gene. It is thought that this process can be subject to epigenetic regulation, but few specific examples of this have been reported. We previously showed that the Mcts2 / H13 locus is subject to genomic imprinting and that alternative polyadenylation of H13 transcripts occurs in an allele-specific manner, regulated by epigenetic mechanisms. Here, we demonstrate that allele-specific polyadenylation occurs at another imprinted locus with similar features. Nap1l5 is a retrogene expressed from the paternally inherited allele, is situated within an intron of a ‘host’ gene Herc3 , and overlaps a CpG island that is differentially methylated between the parental alleles. In mouse brain, internal Herc3 polyadenylation sites upstream of Nap1l5 are used on the paternally derived chromosome, from which Nap1l5 is expressed, whereas a downstream site is used more frequently on the maternally derived chromosome. Ablating DNA methylation on the maternal allele at the Nap1l5 promoter increases the use of an internal Herc3 polyadenylation site and alters exon splicing. These changes demonstrate the influence of epigenetic mechanisms in regulating Herc3 alternative mRNA processing. Internal Herc3 polyadenylation correlates with expression levels of Nap1l5 , suggesting a possible role for transcriptional interference. Similar mechanisms may regulate alternative polyadenylation elsewhere in the genome.

Description: Polyadenylation of eukaryotic mRNAs contributes to stability, transport and translation, and is catalyzed by a large complex of conserved proteins. The Pcf11 subunit of the yeast CF IA factor functions as a scaffold for the processing machinery during the termination and polyadenylation of transcripts. Its partner, Clp1, is needed for mRNA processing, but its precise molecular role has remained enigmatic. We show that Clp1 interacts with the Cleavage–Polyadenylation Factor (CPF) through its N-terminal and central domains, and thus provides cross-factor connections within the processing complex. Clp1 is known to bind ATP, consistent with the reported RNA kinase activity of human Clp1. However, substitution of conserved amino acids in the ATP-binding site did not affect cell growth, suggesting that the essential function of yeast Clp1 does not involve ATP hydrolysis. Surprisingly, non-viable mutations predicted to displace ATP did not affect ATP binding but disturbed the Clp1–Pcf11 interaction. In support of the importance of this interaction, a mutation in Pcf11 that disrupts the Clp1 contact caused defects in growth, 3'-end processing and transcription termination. These results define Clp1 as a bridge between CF IA and CPF and indicate that the Clp1–Pcf11 interaction is modulated by amino acids in the conserved ATP-binding site of Clp1.

Description: We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be –0.24 ± 0.32 G, as compared to –0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2–4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega.

Description: Over the last 40 years variations in the systemic velocity and the observed minus computed time of first conjunction have been observed in the RS Cha binary system. Our goal is to determine the probability for the existence of a third body in this system, and to calculate an orbital solution for this component. A total of 381 high-resolution echelle spectra were obtained at Mount John University Observatory using the 1.0-m McLellan telescope and High Efficiency and Resolution Canterbury University Large Echelle Spectrograph (HERCULES; echelle spectrograph). The spectra were collected during three observing runs occurring over a 15 month period spanning from 2005 November 18 to 2007 February 17, and the data were reduced using the HERCULES reduction software package 2.3. Radial velocities for the 46 echelle orders were generated using Two-Dimensional Correlation, and the velocities from the best 15 orders were selected and used in the calculation of a weighted mean. The weight for each order was determined by generating a preliminary orbital solution for that particular order, using Stern's method, with the rms of the orbital fit used to calculate the associated weight on the order. Systemic velocities for each of the three observing runs were computed by applying a linear regression to the radial velocities of one star against its companion (i.e. V 1 versus V 2 ). The value of the slope and intercept of the regression line are required for calculating the systemic velocity. Analysis of the 381 spectra confirmed the suspected variation of the system velocity during the time-span over which these data were collected. The systemic velocity for each observing run differs significantly (12.13 ± 0.26, 11.41 ± 0.22 and 9.68 ± 0.78 km s –1 ) and combined with four historical (previously published) values they failed the 2 test, and imply a 99.9 per cent confidence that a third body exists. Three possible orbital solutions for the third body, with respect to the close binary, were generated using the historical and current systemic velocity values ( P  = 12.69 ± 0.01 or 24.17 ± 0.01 or 74.45 ± 0.02 d). The orbital solution for the binary was calculated after the effects of the shift in systemic velocity during the course of our data were removed. Values for the period and masses are P  = 1.66988 ± 0.00002 d, M 1  = 1.823 ± 0.012 M and M 2  = 1.764 ± 0.012 M , with the lowest possible mass range obtained from the orbital solutions of the third body ranging from M 3  = 0.30 to 0.52 M .

Description: The TATA binding protein (TBP) is a critical transcription factor used for nucleating assembly of the RNA polymerase II machinery. TBP binds TATA box elements with high affinity and kinetic stability and in vivo is correlated with high levels of transcription activation. However, since most promoters use less stable TATA-less or TATA-like elements, while also competing with nucleosome occupancy, further mechanistic insight into TBP's DNA binding properties and ability to access chromatin is needed. Using bulk and single-molecule FRET, we find that TBP binds a minimal consensus TATA box as a two-state equilibrium process, showing no evidence for intermediate states. However, upon addition of flanking DNA sequence, we observe non-specific cooperative binding to multiple DNA sites that compete for TATA-box specificity. Thus, we conclude that TBP binding is defined by a branched pathway, wherein TBP initially binds with little sequence specificity and is thermodynamically positioned by its kinetic stability to the TATA box. Furthermore, we observed the real-time access of TBP binding to TATA box DNA located within the DNA entry–exit site of the nucleosome. From these data, we determined salt-dependent changes in the nucleosome conformation regulate TBP's access to the TATA box, where access is highly constrained under physiological conditions, but is alleviated by histone acetylation and TFIIA.

Description: We compare different strategies for minimizing the effects of telescope vibrations to the differential piston (optical pathway difference) for the Near-InfraRed/Visible Adaptive Camera and INterferometer for Astronomy (LINC-NIRVANA) at the Large Binocular Telescope (LBT) using an accelerometer feedforward compensation approach. We summarize, why this technology is important for LINC-NIRVANA, and also for future telescopes and already existing instruments. The main objective is outlining a solution for the estimation problem in general and its specifics at the LBT. Emphasis is put on realistic evaluation of the used algorithms in the laboratory, such that predictions for the expected performance at the LBT can be made. Model-based estimation and broad-band filtering techniques can be used to solve the estimation task, and the differences are discussed. Simulation results and measurements are shown to motivate our choice of the estimation algorithm for LINC-NIRVANA. The laboratory setup is aimed at imitating the vibration behaviour at the LBT in general, and the M2 as main contributor in particular. For our measurements, we introduce a disturbance time series which has a frequency spectrum comparable to what can be measured at the LBT on a typical night. The controllers’ ability to suppress vibrations in the critical frequency range of 8–60 Hz is demonstrated. The experimental results are promising, indicating the ability to suppress differential piston induced by telescope vibrations by a factor of about 5 (rms), which is significantly better than any currently commissioned system.

Description: We analyse the Tully–Fisher relation at moderate redshift from the point of view of the underlying stellar populations, by comparing optical and NIR photometry with a phenomenological model that combines population synthesis with a simple prescription for chemical enrichment. The sample comprises 108 late-type galaxies extracted from the FORS Deep Field and William Herschel Deep Field surveys at z   1 (median redshift z  = 0.45). A correlation is found between stellar mass and the parameters that describe the star formation history, with massive galaxies forming their populations early ( z FOR  ~ 3), with star formation time-scales, 1  ~ 4 Gyr, although with very efficient chemical enrichment time-scales ( 2  ~ 1 Gyr). In contrast, the stellar-to-dynamical mass ratio – which, in principle, would track the efficiency of feedback in the baryonic processes driving galaxy formation – does not appear to correlate with the model parameters. On the Tully–Fisher plane, no significant age segregation is found at fixed circular speed, whereas at fixed stellar-to-dynamical mass fraction, age splits the sample, with older galaxies having faster circular speeds at fixed M s / M dyn . Although our model does not introduce any prior constraint on dust reddening, we obtain a strong correlation between colour excess and stellar mass.