Fibrous carcinogens, such as crocidolite asbestos, are known to catalyze many of the same reactions as iron, namely 0_2 consumption, generation of reduced oxygen species, and damage to DNA, such as strand breaks, and modifications of bases. Upon inhalation, fibers are also known to become coated with an iron-rich material. The mechanism by which this iron is bound to fibers in the lung is not known, and the effect of this additional iron on the reactivity of the fibers is also not well understood. The studies described here were undertaken to elucidate the abilities of crocidolite asbestos, in its native, soaked, and iron depleted forms, as well as three varieties of silicon carbide whiskers, to acquire reactive iron on their surfaces. The aim has been to quantitate the amount of iron that can bind in short periods of time, and to measure any changes in biochemical reactivity toward DNA following binding of iron. All forms of the naturally occurring mineral fiber crocidolite, and the man-made mineral fibers (silicon carbide whiskers), were capable of acquiring iron, to varying degrees. Native crocidolite was able to bind up to 57 nmol Fe+ 2/mg crocidolite in one hour, while the iron-depleted form was capable of binding only 5. 5 nmol Fe+ 2/mg crocidolite, and the three varieties of silicon carbide whiskers bound from 2.9 to 29.0 nmol Fe+ 2/mg in the same time period. Following iron binding, the fibers were more capable of forming DNA single-strand breaks. The increase in the ability of the fibers to cause DNA strand breaks was greatest with the silicon carbide whiskers, less with iron depleted crocidolite, and the least with native crocidolite, which is likely because of the inherently high iron content of native crocidolite. Other investigation attempted to determine whether iron could be bound from more complex, physiologically relevant iron-containing solutions where potential iron chelators are abundant. Iron appeared to be acquired even from such complex mixtures as tissue culture media. Following incubation in media, the fibers were more active in catalyzing the formation of DNA strand breaks. An interesting correlation was noted between the abilities of the fibers to cause DNA strand breaks after incubation in tissue culture media and the cytotoxicity of crocidolite to A549 cells grown in the same media.

No description available.

Recently, DNA computing is one of powerful tools that can be designed for solving NP-complete problems. The powers of DNA computing are that it has great ability of massive data storage and it can process those data in parallel. Some of hard problems, such as the traveling salesperson problem and the Hamiltonian cycle problem, have been solved with the brute force method in DNA computing. After DNA computing is performed, all feasible solutions for the problem are stored implicitly in the tubes. However, the correct answer still cannot be extracted or reported absolutely, because that the concentration of the correct solutions might be lower than other bad solutions. In this paper, we will increase the concentration of the correct answer for fault-tolerant ability.

Oldenburg, Universiẗat, Diss., 2003.

No description available.

Allozyme data and DNA strand break frequencies were compared among populations of Pleurocera canaliculatum from five sites with varying mercury contamination on the North Fork Holston River (NFHR) in southwestern Virginia, USA. Allozyme genotype frequencies for four loci were significantly different between populations from the three most highly contaminated sites and those from two lesser contaminated sites. In addition, heterozygosity at three of these loci was significantly lower in the populations from the most highly contaminated sites. The DNA strand break frequency was significantly correlated to whole-body total mercury concentration in snails from three sites. These data add to the evidence supporting the use of DNA strand breakage as an indicator of chemical contamination and the use of allozyme analysis as a marker of contamination and possible selection for pollution resistance. However, the relationship between contaminant-induced changes in the genetic variation of enzymes of central metabolism and the functionalities upon which selection for resistance may act remain unclear, and mechanisms other than selection for resistance must be considered. Use of enzymes from other biochemical pathways may be appropriate for other species or for those under other chemical pollution pressures.

Homologous recombination is critical for generating genetic variation in living organisms by exchange and rearrangement of DNA. Most of our knowledge about homologous recombination is limited to processes in bacteria or in eukaryotic nuclei. In E. coli, homologous recombination is dependent on the RecA protein. Higher plant chloroplasts have RecA-like strand exchange activity. However, little is known about these mechanisms in higher plant mitochondria. I have detected a RecA-like strand exchange activity in soybean mitochondria. This activity forms joint molecules in the presence of ATP, Mg2+, and homologous DNA substrates. In addition, the E. coli single-stranded DNA binding (SSB) protein is a non-sequence-specific DNA binding protein that functions as an accessory factor for RecA protein-promoted strand exchange reactions. Our lab has identified an Arabidopsis homologue of E. coli SSB that is targeted to mitochondria (mtSSB). The results of my research shows the mtSSB protein has the same properties as the E. coli SSB protein and it can stimulate the E. coli RecA protein-promoted strand exchange reactions. DNA helicases utilize the energy of ATP to separate the two parental DNA strands at the replicating fork or during recombinational strand exchange. Although higher plant chloroplast helicase activity has been reported, no such activity has heretofore been identified in higher plant mitochondria. We report the characterization of a plant mitochondrial DNA helicase isolated from soybean leaves. ATP is required for this enzyme and this enzyme poorly utilizes any other NTPs or dNTPs. The enzyme requires Mg2+ for activity. This enzyme only has 3' to 5'unwinding activity. The optimal conditions for mitochondrial DNA helicase are 2 mM ATP, 8 to 10 mM Mg2+,100 to 200 mM NaCl and 37-42 oC incubation for one hour or longer time.

Hepatitis E virus (HEV) is the major cause of enterically transmitted non-A, non-B hepatitis in many developing countries, and is also endemic in many industrialized countries. Due to the lack of an effective cell culture system and a practical animal model, the mechanisms of HEV pathogenesis and replication are poorly understood. It has been speculated that HEV replicates in sites other than the liver. Since HEV is presumably fecal-orally transmitted it is unclear how the virus reaches the liver and extrahepatic replication could be a possible explanation. The recent identification of swine HEV from pigs affords us an opportunity to systematically study HEV replication in a swine model. We experimentally infected specific-pathogen-free (SPF) pigs with two strains of HEV: swine HEV and the US-2 strain of human HEV. Eighteen pigs (group 1) were each inoculated intravenously with swine HEV, nineteen pigs (group 2) with the US-2 strain of human HEV, and seventeen pigs (group 3) as uninoculated controls. To identify the potential extrahepatic sites of HEV replication using the swine model, two pigs from each group were necropsied at 3, 7, 14, 20, 27, and 55 days post inoculation (DPI). Thirteen different types of tissues and organs were collected from each necropsied animal. Reverse transcriptase PCR (RT-PCR) was used to detect the presence of positive strand HEV RNA in each tissue collected during necropsy at different DPIs. A negative strand-specific RT-PCR was standardized and used to detect the replicative, negative-strand of HEV RNA from tissues that tested positive for the positive strand RNA. As expected, positive strand HEV RNA was detected in almost every type of tissue at some time point during viremic period between 3 and 27 DPI. Positive-strand HEV RNA was still detectable in some tissues in the absence of serum HEV RNA from both swine and human HEV inoculated pigs. However, replicative, negative strand of HEV RNA was detected primarily in the small intestine, lymph nodes, colon, and liver. Our results demonstrate for the first time that HEV replicates in tissues other than the liver and that the gastrointestinal tract is also the target of virus infection. The data from this study may have important implications for HEV pathogenesis, xenotransplantation, and the development of an in vitro cell culture system for HEV. / Master of Science

This thesis investigates the repair of impact-damaged prestressed concrete bridge girders with strand splices and fabric-reinforced cementitious matrix systems, specifically for repair of structural damage to the underside of an overpass bridge girder due to an overheight vehicle collision. Collision damage to bridges can range from minor to catastrophic, potentially requiring repair or replacement of a bridge girder. This thesis investigates the performance of two different types of repair methods for flexural applications: strand splice repair, which is a traditional repair method that is often utilized, and fabric-reinforced cementitious matrix repair, which is a relatively new repair method. The overarching goal of this project was to provide guidance for assessment and potential repair of impact-damaged girders. Prestressed concrete girders were tested to failure in flexure in this research. After a control test to establish a baseline for comparison, five tests were performed involving damaging a girder, repairing it using one of the repair methods, and testing it to failure. These tests showed that both strand splice repairs and fabric-reinforced cementitious matrix repairs can adequately restore the strength of an impact-damaged girder when up to 10% of the prestressing strands are severed. Combined repairs can also be a viable option if more than 10% of the prestressing strands are severed, though as the damage gets more severe, girder replacement becomes a more attractive option. / Master of Science / This thesis investigates the structural repair of impact-damaged prestressed concrete bridge girders. Impact damage to these structural elements is most commonly an overheight vehicle colliding with the underside of an overpass bridge girder on a roadway. Damage to the structure can range from minor to catastrophic. Though more destructive impacts require replacement of the girder or entire bridge structure, repair of the damaged girder is possible in some cases. This thesis studies two different methods of repair of these impact-damaged girders: strand splices and fabric-reinforced cementitious matrix. Full-scale prestressed concrete girders were tested to failure in this research. A total of five tests were performed involving damaging a girder, repairing it using one of the repair methods, and testing it to failure. These tests showed that both repair methods can adequately restore the strength of an impact-damaged girder for minor to moderate structural damage. The overarching goal of this project was to provide guidance for assessment and potential repair of impact-damaged girders.

Doctor of Philosophy / Department of Civil Engineering / Kyle A. Riding / ASTM recently adopted the Standard Test Method for Evaluating Bond of Seven-Wire Steel Prestressing Strand as ASTM A1081, a pull-out test procedure developed for verifying the ability of steel strands to bond to cementitious materials prior to their use as tensile reinforcement in prestressed concrete sections. The required by ASTM International precision and bias statement has not been developed for this test method. In addition, a minimum threshold value that will ensure only adequately bonding strand sources will be accepted has not yet been applied to ASTM A1081. The test method was developed after findings that prestressing steel strand sources of identical type and grade vary significantly as far as their bonding capacity. Bond is a crucial aspect of the prestressing force being transferred into the concrete, and insufficient bonding action can result in the prestressed concrete section lacking in capacity to sustain the loads that it was designed for. After an initial survey of the pull-out strength of North American Strand in mortar, three strands of differing pull-out strengths were selected for inclusion in further testing. A precision and bias statement for ASTM A1081 was developed by first performing ruggedness testing to determine how the results are affected by allowable variations in methods and materials, and followed by an inter-laboratory study to determine the reproducibility of the test method. Once the precision and bias statement for the standard test method was developed, the same strand sources were tested for their performance in concrete beams. Statistical analysis of the flexural beam testing data and correlation with the prestressing strand sources’ ASTM A1081 test results was performed, and the industry was provided with minimum acceptance criteria for prestressing strand tested by ASTM A1081, along with recommendations regarding the standard test method and aspects of prestressed concrete design.