DNA Ligase C and Prim-PolC participate in base excision repair in mycobacteria

Prokaryotic Ligase D is a conserved DNA repair apparatus processing DNA double-strand breaks in stationary phase. An orthologous Ligase C (LigC) complex also co-exists in many bacterial species but its function is unknown. Here, we show that the LigC complex interacts with core BER enzymes in vivo and demonstrate that together these factors constitute an excision repair apparatus capable of repairing damaged bases and abasic sites. The polymerase component, which contains a conserved C-terminal structural loop, preferentially binds to and fills-in short gapped DNA intermediates with RNA and LigC ligates the resulting nicks to complete repair. Components of the LigC complex, like LigD, are expressed upon entry into stationary phase and cells lacking either of these pathways exhibit increased sensitivity to oxidising genotoxins. Together, these findings establish that the LigC complex is directly involved in an excision repair pathway(s) that repairs DNA damage with ribonucleotides during stationary phase

Molecular basis for DNA repair synthesis on short gaps by mycobacterial Primase-Polymerase C

Cells utilise specialized polymerases from the Primase-Polymerase (Prim-Pol) superfamily to maintain genome stability. Prim-Pol’s function in genome maintenance pathways including replication, repair and damage tolerance. Mycobacteria contain multiple Prim-Pols required for lesion repair, including Prim-PolC that performs short gap repair synthesis during excision repair. To understand the molecular basis of Prim-PolC’s gap recognition and synthesis activities, we elucidated crystal structures of pre- and post-catalytic complexes bound to gapped DNA substrates. These intermediates explain its binding preference for short gaps and reveal a distinctive modus operandi called Synthesis-dependent Template Displacement (STD). This mechanism enables Prim-PolC to couple primer extension with template base dislocation, ensuring that the unpaired templating bases in the gap are ushered into the active site in an ordered manner. Insights provided by these structures establishes the molecular basis of Prim-PolC’s gap recognition and extension activities, while also illuminating the mechanisms of primer extension utilised by closely related Prim-Pols

Structure of complex oxide nanoparticles in a Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) ODS RAF steel

One of the most crucial steps in the development of oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels is the engineering of their microstructure, which includes control of the type and size of oxide nanoparticles. In this work, the composition and crystal structure of oxide particles grown in the Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) ODS RAF steel were characterized using advanced spectroscopic and microscopic techniques. The electron energy loss spectroscopic mapping has shown presence of numerous fine Y-Ti-O oxides but also larger Cr-Ti-O and Cr-N particles among those extracted from the bulk samples. In addition, atom probe tomography of the as-compacted ODS RAF samples revealed a uniform spatial distribution of fine oxides containing mainly Y, Ti, and O. The orthorhombic YTiO3, having distorted perovskite structure, was identified in all analyzed oxides using HR-STEM and diffraction pattern analysis. (C) 2013 Elsevier B.V. All rights reserved

Statistical analysis of oxides particles in ODS ferritic steel using advanced electron microscopy

In this work a combination of advanced transmission electron microscopy and spectroscopy techniques enabled a statistically significant analysis of various types of few nanometer size oxides particles in Fe-14Cr-2W-O.3Ti-0.3Y(2)O(3) ferritic steel. These methods include a scanning TEM with EDS and EFTEM coupled with EELS. In addition, principal component analysis was applied to the chemical maps obtained by EFTEM, which drastically improved the signal to noise ratio. Three types of particles were identified in a size range from 2 to 300 nm, namely Cr-Ti-O, Y-O and Y-Ti-O particles, with an average size of 33,16 and 8 nm, respectively. The Cr-Ti-O particles contain Y and Ti enriched zones, which were not observed previously. The EFTEM analysis showed that the titanium addition leads to formation of Y-Ti-O nanoparticles, which constitute 84% of the oxides but also precipitation of larger Cr-Ti-O. The presence of small amount of Y-O particles indicated a not sufficient amount of Ti available for reaction during mechanical alloying or consolidation. (C) 2012 Elsevier B.V. All rights reserved

Microstructural stability of ODS steels in cyclic loading

The remarkable microstructural stability of high chromium steels prepared by powder metallurgy and strengthened by dispersion of nanometric yttrium oxides in cyclic loading at high temperatures is reported. Contrary to the continuous cyclic softening and profound changes in the microstructure during fatigue of common high chromium steels, the addition of 0.3wt% Y2O3 stabilizes the microstructure and significantly reduces cyclic softening of investigated steels. The evolution of microstructure as a result of fatigue loading at room temperature, 650 and 750 degrees C, was examined by means of transmission electron microscopy. Only minor changes in the microstructure were detected. The stability of oxide particles after high-temperature exposure was confirmed by energy dispersion spectroscopy chemical analysis. The microstructural features are discussed in relation to the cyclic behaviour of the oxide dispersion strengthened steels. The analysis of the hysteresis loop indicates that oxide nanoclusters are intersected and dissolved in slip bands of ODS Eurofer steel. This process contributes to cyclic softening