http://hdl.handle.net/10092/24 Wed, 15 May 2013 04:24:38 GMT 2013-05-15T04:24:38Z http://hdl.handle.net/10092/7715 Title: Adaptive evolution by recombination is not associated with increased mutation rates in Maize streak virus Authors: Monjane, A.L.; Pande, D.; Lakay, F.; Shepherd, D.N.; van der Walt, E.; Lefeurve, P.; Lett, J-M.; Varsani, A.; Rybicki, E.P.; Martin, D.P. Abstract: Background Single-stranded (ss) DNA viruses in the family Geminiviridae are proving to be very useful in real-time evolution studies. The high mutation rate of geminiviruses and other ssDNA viruses is somewhat mysterious in that their DNA genomes are replicated in host nuclei by high fidelity host polymerases. Although strand specific mutation biases observed in virus species from the geminivirus genus Mastrevirus indicate that the high mutation rates in viruses in this genus may be due to mutational processes that operate specifically on ssDNA, it is currently unknown whether viruses from other genera display similar strand specific mutation biases. Also, geminivirus genomes frequently recombine with one another and an alternative cause of their high mutation rates could be that the recombination process is either directly mutagenic or produces a selective environment in which the survival of mutants is favoured. To investigate whether there is an association between recombination and increased basal mutation rates or increased degrees of selection favoring the survival of mutations, we compared the mutation dynamics of the MSV-MatA and MSV-VW field isolates of Maize streak virus (MSV; Mastrevirus), with both a laboratory constructed MSV recombinant, and MSV recombinants closely resembling MSV-MatA. To determine whether strand specific mutation biases are a general characteristic of geminivirus evolution we compared mutation spectra arising during these MSV experiments with those arising during similar experiments involving the geminivirus Tomato yellow leaf curl virus (Begomovirus genus). Results Although both the genomic distribution of mutations and the occurrence of various convergent mutations at specific genomic sites indicated that either mutation hotspots or selection for adaptive mutations might elevate observed mutation rates in MSV, we found no association between recombination and mutation rates. Importantly, when comparing the mutation spectra of MSV and TYLCV we observed similar strand specific mutation biases arising predominantly from imbalances in the complementary mutations G → T: C → A. Conclusions While our results suggest that recombination does not strongly influence mutation rates in MSV, they indicate that high geminivirus mutation rates are at least partially attributable to increased susceptibility of all geminivirus genomes to oxidative damage while in a single stranded state. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10092/7715 2012-01-01T00:00:00Z http://hdl.handle.net/10092/7379 Title: Single-Pulse Pulsed Laser Polymerization–Electron Paramagnetic Resonance Investigations into the Termination Kinetics of n-Butyl Acrylate Macromonomers Authors: Barth, J.; Buback, M.; Barner-Kowollik, C.; Junkers, T.; Russell, G.T. Abstract: The termination of model mid-chain radicals (MCRs), which mimic radicals that occur in acrylate polymerization over a broad range of reaction conditions, has been studied by singlepulse pulsed-laser polymerization (SP PLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The model radicals were generated by initiator-fragment addition to acrylic macromonomers that were preformed prior to the kinetic experiments, thus enabling separation of termination from the propagation reaction, for these model radicals propagate sparingly, if at all, on the timescale of SP-PLP experiments. Termination rate coefficients of the MCRs were determined in the temperature range 0–60 °C in acetonitrile and butyl propionate solution as well as in bulk macromonomer over 0–100 °C. Termination rate coefficients slightly below those of the corresponding secondary radicals were deduced, demonstrating the relatively high termination activity of this species, even when undergoing MCR-MCR termination. For chain length 10, a reduction by a factor of 6 is observed. Unusually high activation energies were found for the termination rate coefficient in these systems, with 35 kJ mol⁻¹ being determined for bulk macromonomer. Description: The definitive version is available at www3.interscience.wiley.com Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10092/7379 2012-01-01T00:00:00Z http://hdl.handle.net/10092/7350 Title: Determining the order of a molecular point group Authors: Williamson, B.E. Abstract: Conventional methods of identifying the point group of a molecule require skills in finding symmetry elements and operations. A useful aid to error checking is an ability to determine the order of a group purely from its label. To this end, Curnow has promulgated a set of simple empirical rules. In this article, Curnow’s rules are substantiated using simple geometric considerations from the basis of point group generators. The proof is provided in a form that will be accessible to undergraduate chemistry students and their teachers Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10092/7350 2011-01-01T00:00:00Z http://hdl.handle.net/10092/7287 Title: The seismic impact on chemistry teaching and research at University of Canterbury Authors: Williamson, B.; Hartshorn, R. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10092/7287 2012-01-01T00:00:00Z