Nozomi Nakanishi

Human endonuclease V is a ribonuclease specific for inosine-containing RNA

Deamination of DNA bases can create missense mutations predisposing humans to cancer and also interfere with other basic molecular genetic processes; this deamination generates deoxyinosine from deoxyadenosine. In Escherichia coli, the highly conserved endonuclease V is involved in alternative excision repair that removes deoxyinosine from DNA. However, its exact activities and roles in humans are unknown. Here we characterize the FLJ35220 protein, the human homologue of E. coli endonuclease V, hEndoV as a ribonuclease specific for inosine-containing RNA. hEndoV preferentially binds to RNA and efficiently hydrolyses the second phosphodiester bond located 3′ to the inosine in unpaired inosine-containing ssRNA regions in dsRNA. It localizes to the cytoplasm in cells. The ribonuclease activity is promoted by Tudor staphylococcal nuclease and detected on inosine-containing dsRNA created by the action of adenosine deaminases acting on RNA. These results demonstrate that hEndoV controls the fate of inosine-containing RNA in humans.

Effects of DNA lesions on the transcription reaction of mitochondrial RNA polymerase: implications for bypass RNA synthesis on oxidative DNA lesions

Oxidative DNA lesions inhibit the transcription of RNA polymerase II, but in the presence of transcription elongation factors, the transcription can bypass the lesions. Single-subunit mitochondrial RNA polymerase (mtRNAP) catalyses the synthesis of essential transcripts in mitochondria where reactive oxidative species (ROS) are generated as by-products. The occurrence of RNA synthesis by mtRNAP at oxidative DNA lesions remains unknown. Purified mtRNAP and a complex of RNA primer/DNA template containing a single DNA lesion, such as ROS-induced 8-oxoguanine (8-oxoG), two isomeric thymine glycols (5R-Tg or 5S-Tg), the UV-induced cis-syn cyclobutane pyrimidine dimer (CPD) and the pyrimidine(6-4)pyrimidone photoproduct (6-4pp), or a spontaneous common DNA lesion, a base-loss-induced apurinic/apyrimidinic (AP) site, were used for in vitro RNA synthesis assays. In this report, we show that mtRNAP bypassed the oxidative DNA lesions of non-bulky 8-oxoG and 5R-Tg and 5S-Tg with pausing sites but did not bypass the UV-induced DNA lesions and the AP site. The bacteriophage T7 phage RNA polymerase, which is homologous to mtRNAP, bypassed 8-oxoG but stalled at 5R-Tg and 5S-Tg. As expected, although translesion RNA synthesis in 8-oxoG on the DNA templates generated incorrect transcripts with a G:C to T:A transversion, the synthesis in Tg could lead to the correct transcripts with no transcriptional mutagenesis. Collectively, these data suggest that mtRNAP may tolerate the mitochondrial genome containing oxidative DNA lesions induced by ROS from the side effects of an ATP generation reaction.

The Development of a Ti-6Al-4V Alloy via Oxygen Solid Solution Strengthening for Aerospace and Defense Applications

The high cost of titanium has historically prevented widespread use in military ground vehicles. Two strategies to make this material more cost effective and viable are to reduce the cost of titanium armors or to improve the ballistic performance of titanium and reduce the amount of material required. This paper investigates the latter strategy. Mixtures of titanium powders and TiO2 particles were employed as starting materials and consolidated by spark plasma sintering (SPS) and hot extrusion. The content of TiO2 particles was 0~1.5% of the mass mixture. Solidification of oxygen atoms (from TiO2 particles) into Ti matrix occurred at 1073K for 1800 seconds in a vacuum. Tensile testing showed that Tensile Strength (TS) and Yield Strength (YS) increased in proportion to TiO2 content but elongation decreased slightly with increased TiO2 content. Extruded pure Ti powder material with 1.5% TiO2 particles produced 1040 MPa TS, 902 MPa YS and 25.1% elongation when tested. When using Ti-6Al-4V (Ti-64) alloy powders with 0.5% TiO2 particles, the final extruded Ti-64 powder bars with oxygen solid solution showed 1226 MPa TS and 22.7% elongation. Initial ballistic evaluation showed the Ti-64 powder bars with 0.5% TiO2 particles yielded a marked improvement over the conventionally rolled Ti-64 alloy plate.

Evaluation of Initial Corrosion Phenomenon of Magnesium Alloys by SKPFM

Magnesium (Mg) has the lowest standard electrode potential in structural materials, and then it easily corroded for that property contacting with other metals. The corrosion resistance of Mg alloys was generally investigated by conducting saltwater immersion test, salt spray test, and electrochemical corrosion test. However, these tests give only macroscopic information but don’t give microscopic (i.e. galvanic corrosion at the interface). So, the origin of galvanic corrosion at the interface between dispersoids and a-Mg in Mg alloys was investigated for fundamental clarification. In this paper, the surface potential difference (VSPD) at the interface between dispersoids and a-Mg using AZ91D Mg alloy is measured by using Scanning Kelvin Probe Force Microscope (SKPFM). Surface potential of pure metals measured by SKPFM had good correlation with standard electrode potential (SEP), and then VSPD also positively correlated with difference of SEP. Salt water immersion test was conducted using AZ91D in order to compare VSPD with corrosion phenomenon. Topographic map around the interface between dispersoids and a-Mg was measured by using AFM after corrosion test. Corroded phase corresponded to the anodic phase indicated by surface potential.