612 research outputs found
Telomeric circles are abundant in the stn1-M1 mutant that maintains its telomeres through recombination
Some human cancers maintain their telomeres using the alternative lengthening of telomeres (ALT) mechanism; a process thought to involve recombination. Different types of recombinational telomere elongation pathways have been identified in yeasts. In senescing yeast telomerase deletion (ter1-Δ) mutants with very short telomeres, it has been hypothesized that copying a tiny telomeric circle (t-circle) by a rolling circle mechanism is the key event in telomere elongation. In other cases more closely resembling ALT cells, such as the stn1-M1 mutant of Kluyveromyces lactis, the telomeres appear to be continuously unstable and routinely reach very large sizes. By employing two-dimensional gel electrophoresis and electron microscopy, we show that stn1-M1 cells contain abundant double stranded t-circles ranging from ∼100 to 30 000 bp in size. We also observed small single-stranded t-circles, specifically composed of the G-rich telomeric strand and tailed circles resembling rolling circle replication intermediates. The t-circles most likely arose from recombination events that also resulted in telomere truncations. The findings strengthen the possibility that t-circles contribute to telomere maintenance in stn1-M1 and ALT cells
Making the Most of Citation Data: The Integration of Thomson Reuters Web of Science and UWA's Research Management System, Socrates
In late 2006 The University of Western Australia launched Socrates, an online application designed to draw data from key research information systems, in order for the University to prepare portfolios for the Research Quality Framework (RQF). Socrates also incorporates bibliographic and citation data from Thomson Reuters’ Web of Science (WoS) using the web services interface (API). This presentation focuses upon the utilisation of Thomson Reuters’ data within Socrates. The benefits of importing Thomson Reuters’ data, including reducing the workload associated with the annual HERDC publications collection, and using imported research tags to trace the level of publication within specific disciplines, are explored. The presentation also outlines the technical problems faced by Socrates with regards to matching citation data imported from the WOS to data from the UWA Publications Database. Overall, it is argued that by drawing data from the WOS, Socrates is able to provide a detailed analysis of UWA’s indexed publications at a university, organisational unit and individual level, thereby shedding significant light on the University’s research output performance
Recombination at Long Mutant Telomeres Produces Tiny Single- and Double-Stranded Telomeric Circles
Recombinational telomere elongation (RTE) known as alternate lengthening of telomeres is the mechanism of telomere maintenance in up to 5 to 10% of human cancers. The telomeres of yeast mutants lacking telomerase can also be maintained by recombination. Previously, we proposed the roll-and-spread model to explain this elongation in the yeast Kluveromyces lactis. This model suggests that a very small (∼100-bp) circular molecule of telomeric DNA is copied by a rolling circle event to generate a single long telomere. The sequence of this primary elongated telomere is then spread by recombination to all remaining telomeres. Here we show by two-dimensional gel analysis and electron microscopy that small circles of single- and double-stranded telomeric DNA are commonly made by recombination in a K. lactis mutant with long telomeres. These circles were found to be especially abundant between 100 and 400 bp (or nucleotides). Interestingly, the single-stranded circles consist of only the G-rich telomeric strand sequence. To our knowledge this is the first report of single-stranded telomeric circles as a product of telomere dysfunction. We propose that the small telomeric circles form through the resolution of an intratelomeric strand invasion which resembles a t-loop. Our data reported here demonstrate that K. lactis can, in at least some circumstances, make telomeric circles of the very small sizes predicted by the roll-and-spread model. The very small circles seen here are both predicted products of telomere rapid deletion, a process observed in both human and yeast cells, and predicted templates for roll-and-spread RTE
Many Body Theory of Charge Transfer in Hyperthermal Atomic Scattering
We use the Newns-Anderson Hamiltonian to describe many-body electronic
processes that occur when hyperthermal alkali atoms scatter off metallic
surfaces. Following Brako and Newns, we expand the electronic many-body
wavefunction in the number of particle-hole pairs (we keep terms up to and
including a single particle-hole pair). We extend their earlier work by
including level crossings, excited neutrals and negative ions. The full set of
equations of motion are integrated numerically, without further approximations,
to obtain the many-body amplitudes as a function of time. The velocity and
work-function dependence of final state quantities such as the distribution of
ion charges and excited atomic occupancies are compared with experiment. In
particular, experiments that scatter alkali ions off clean Cu(001) surfaces in
the energy range 5 to 1600 eV constrain the theory quantitatively. The
neutralization probability of Na ions shows a minimum at intermediate
velocity in agreement with the theory. This behavior contrasts with that of
K, which shows ... (7 figures, not included. Figure requests:
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