Microstructure of Spark Plasma-Sintered Silicon Nitride Ceramics.

The microstructure and phase composition of the high-content AlO-YO-doped spark plasma-sintered silicon nitride were investigated. Fully dense silicon nitride ceramics with a typical α-SiN equiaxed structure with average grain size from 200 to 530 nm, high elastic modulus of 288 GPa, and high hardness of 2038 HV were spark plasma sintered (SPSed) at 1550 °C. Silicon nitride with elongated β-SiN grains, higher hardness of 1800 HV, density of 3.

Microstructure and Phase Composition of Cold Isostatically Pressed and Pressureless Sintered Silicon Nitride.

The microstructure and physical properties of new Y2O3 and Al2O3 oxide-doped silicon nitride ceramics fabricated by cold isostatic pressing and free sintering were investigated. The phase composition of produced material was also studied by X-ray diffraction at room and elevated temperature. The fabricated ceramics featured a microstructure of Si5AlON7 grains with a fine-grained α-Si3N4 with a small amount of Y2SiAlON5.

Involvement of the beta clamp in methyl-directed mismatch repair in vitro.

We have examined function of the bacterial beta replication clamp in the different steps of methyl-directed DNA mismatch repair. The mismatch-, MutS-, and MutL-dependent activation of MutH is unaffected by the presence or orientation of loaded beta clamp on either 3' or 5' heteroduplexes. Similarly, beta is not required for 3' or 5' mismatch-provoked excision when scored in the presence of gamma complex or in the presence of gamma complex and DNA polymerase III core components.

DNA-bound redox activity of DNA repair glycosylases containing [4Fe-4S] clusters.

MutY and endonuclease III, two DNA glycosylases from Escherichia coli, and AfUDG, a uracil DNA glycosylase from Archeoglobus fulgidus, are all base excision repair enzymes that contain the [4Fe-4S](2+) cofactor. Here we demonstrate that, when bound to DNA, these repair enzymes become redox-active; binding to DNA shifts the redox potential of the [4Fe-4S](3+/2+) couple to the range characteristic of high-potential iron proteins and activates the proteins toward oxidation. Electrochemistry on DNA-modified electrodes reveals potentials for Endo III and AfUDG of 58 and 95 mV versus NHE, respectively, comparable to 90 mV for MutY bound to DNA.