All-sky Radio SETI

Over the last decade, Aperture Arrays (AA) have successfully replaced parabolic dishes as the technology of choice at low radio frequencies - good examples are the MWA, LWA and LOFAR. Aperture Array based telescopes present several advantages, including sensitivity to the sky over a very wide field-of-view. As digital and data processing systems continue to advance, an all-sky capability is set to emerge, even at GHz frequencies. We argue that assuming SETI events are both rare and transitory in nature, an instrument with a large field-of-view, operating around the so-called water-hole (1-2 GHz), might offer several advantages over contemporary searches. Sir Arthur C. Clarke was the first to recognise the potential importance of an all-sky radio SETI capability, as presented in his book, Imperial Earth. As part of the global SKA (Square Kilometre Array) project, a Mid-Frequency Aperture Array (MFAA) prototype known as MANTIS (Mid- Frequency Aperture Array Transient and Intensity-Mapping System) is now being considered as a precursor for SKA-2. MANTIS can be seen as a first step towards an all-sky radio SETI capability at GHz frequencies. This development has the potential to transform the field of SETI research, in addition to several other scientific programmes.Comment: 7 pages, 4 figures, accepted for publication, Proceedings of Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in Stellenbosch 25-27 May 2016. Comments welcom

The latest on Apertif

We describe a Phased Array Feed (PAF) system, called Apertif, which will be installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous field of view of the WSRT 8 deg^2 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications ranging from deep surveys of the northern sky of HI and OH emission and polarised continuum to efficient searches for pulsars and transients. We present results obtained with a prototype PAF installed in one of the WSRT dishes. These results demonstrate that at decimetre wavelengths PAFs have excellent performance and that even for a single beam on the sky they outperform single feed radio dishes. PAFs turn radio telescopes into very effective survey instruments. Apertif is now fully funded and the community is invited to express their interest in using Apertif (http://www.astron.nl/radio-observatory/call-expressions-interest-apertif-surveys )Comment: Talk presented at 'A New Golden Age for Radio Astronomy', International SKA Forum 2010, 10-14 June 2010, Hof van Saksen, N

Apertif - the focal-plane array system for the WSRT

We describe a focal plane array (FPA) system, called Apertif, that is being developed for the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is to increase the instantaneous field of view of the WSRT by a factor of 37 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications such as deep imaging surveys of the northern sky of HI and OH emission, of the polarised continuum and efficient searches for pulsars and transients. Such surveys will detect the HI in more than 100,000 galaxies out to z = 0.4, will allow to determine the detailed structure of the magnetic field of the Galaxy, and will discover more than 1,000 pulsars. We present experimental results obtained with a prototype FPA installed in one of the WSRT dishes. These results demonstrate that FPAs do have the performance that is required to make all these surveys possible.Comment: Presented at Widefield Science and Technology for the SKA, SKADS Conference 2009, Chateau de Limelette, Belgium, 4-6 novemer 2009; 7 page

DNA damage stabilizes interaction of CSB with the transcription elongation machinery

The Cockayne syndrome B (CSB) protein is essential for transcription-coupled DNA repair (TCR), which is dependent on RNA polymerase II elongation. TCR is required to quickly remove the cytotoxic transcription-blocking DNA lesions. Functional GFP-tagged CSB, expressed at physiological levels, was homogeneously dispersed throughout the nucleoplasm in addition to bright nuclear foci and nucleolar accumulation. Photobleaching studies showed that GFP-CSB, as part of a high molecular weight complex, transiently interacts with the transcription machinery. Upon (DNA damage-induced) transcription arrest CSB binding these interactions are prolonged, most likely reflecting actual engagement of CSB in TCR. These findings are consistent with a model in which CSB monitors progression of transcription by regularly probing elongation complexes and becomes more tightly associated to these complexes when TCR is active

Different SWI/SNF complexes coordinately promote R-loop- and RAD52-dependent transcription-coupled homologous recombination

The SWI/SNF family of ATP-dependent chromatin remodeling complexes is implicated in multiple DNA damage response mechanisms and frequently mutated in cancer. The BAF, PBAF and ncBAF complexes are three major types of SWI/SNF complexes that are functionally distinguished by their exclusive subunits. Accumulating evidence suggests that double-strand breaks (DSBs) in transcriptionally active DNA are preferentially repaired by a dedicated homologous recombination pathway. We show that different BAF, PBAF and ncBAF subunits promote homologous recombination and are rapidly recruited to DSBs in a transcription-dependent manner. The PBAF and ncBAF complexes promote RNA polymerase II eviction near DNA damage to rapidly initiate transcriptional silencing, while the BAF complex helps to maintain this transcriptional silencing. Furthermore, ARID1A-containing BAF complexes promote RNaseH1 and RAD52 recruitment to facilitate R-loop resolution and DNA repair. Our results highlight how multiple SWI/SNF complexes perform different functions to enable DNA repair in the context of actively transcribed genes.</p

A very brief description of LOFAR - the Low Frequency Array

LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30-240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): 1) detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2) low-frequency surveys of the sky with of order $10^8$ expected new sources; 3) all-sky monitoring and detection of transient radio sources such as gamma-ray bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 10^21 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.Comment: 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van der Hucht, e

Nuclear Dynamics of PCNA in DNA Replication and Repair

The DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) is central to both DNA replication and repair. The ring-shaped homotrimeric PCNA encircles and slides along double-stranded DNA, acting as a “sliding clamp” that localizes proteins to DNA. We determined the behavior of green fluorescent protein-tagged human PCNA (GFP-hPCNA) in living cells to analyze its different engagements in DNA replication and repair. Photobleaching and tracking of replication foci revealed a dynamic equilibrium between two kinetic pools of PCNA, i.e., bound to replication foci and as a free mobile fraction. To simultaneously monitor PCNA action in DNA replication and repair, we locally inflicted UV-induced DNA damage. A surprisingly longer residence time of PCNA at damaged areas than at replication foci was observed. Using DNA repair mutants, we showed that the initial recruitment of PCNA to damaged sites was dependent on nucleotide excision repair. Local accumulation of PCNA at damaged regions was observed during all cell cycle stages but temporarily disappeared during early S phase. The reappearance of PCNA accumulation in discrete foci at later stages of S phase likely reflects engagements of PCNA in distinct genome maintenance processes dealing with stalled replication forks, such as translesion synthesis (TLS). Using a ubiquitination mutant of GFP-hPCNA that is unable to participate in TLS, we noticed a significantly shorter residence time in damaged areas. Our results show that changes in the position of PCNA result from de novo assembly of freely mobile replication factors in the nucleoplasmic pool and indicate different binding affinities for PCNA in DNA replication and repair