A single-channel virtual receiving array using a time-reversal chaotic cavity.

Chaotic reverberation in a cavity, when coupled with time reversal acoustics, can be harnessed to build a perfect time-reversal mirror for transmitting and receiving highly focused sounds with a small number of transducers. In this article, a virtual receiving array, comprised of a single receiving transducer and a chaotic cavity, is developed based on time reversal processing of the reverberation inside the cavity. A prototype array, having 10 × 10 virtual receiving elements, is built and evaluated against a comparable physical array in terms of its localization and waveform reproduction capabilities.

Development of disposable membrane hydrophones for a frequency range from 1MHz to 10MHz.

A method for fabricating disposable membrane hydrophones is presented. The disposable hydrophones are intended for onetime use in such damaging environments as chemically contaminating fluids and high-amplitude (peak amplitude ∼100MPa) shock wave fields, where the use of commercial membrane hydrophones is not recommended. Fabrication of a hydrophone is done using only off-the-shelf components and hand tools, which translates into ease of fabrication and orders-of-magnitude reduction in unit cost.

Effect of alumina composition and surface integrity in alumina/epoxy composites on the ultrasonic attenuation properties.

We report a method of fabricating backing blocks for ultrasonic imaging transducers, using alumina/epoxy composites. Backing blocks contain scatterers such as alumina particles interspersed in the epoxy matrix for the effective scattering and attenuation of ultrasound. Here, the surface integrity can be an issue, where the composite material may be damaged during machining because of differences in strength, hardness and brittleness of the hard alumina particles and the soft epoxy matrix.

Mechanism of Werner DNA helicase: POT1 and RPA stimulates WRN to unwind beyond gaps in the translocating strand.

WRN belongs to the RecQ family of DNA helicases and it plays a role in recombination, replication, telomere maintenance and long-patch base excision repair. Here, we demonstrate that WRN efficiently unwinds DNA substrates containing a 1-nucleotide gap in the translocating DNA strand, but when the gap size is increased to 3-nucleotides unwinding activity significantly declines. In contrast, E.

Intrinsic ssDNA annealing activity in the C-terminal region of WRN.

Werner syndrome (WS) is a rare autosomal recessive disorder in humans characterized by premature aging and genetic instability. WS is caused by mutations in the WRN gene, which encodes a member of the RecQ family of DNA helicases. Cellular and biochemical studies suggest that WRN plays roles in DNA replication, DNA repair, telomere maintenance, and homologous recombination and that WRN has multiple enzymatic activities including 3' to 5' exonuclease, 3' to 5' helicase, and ssDNA annealing.

Human embryonic stem cells have enhanced repair of multiple forms of DNA damage.

Embryonic stem cells need to maintain genomic integrity so that they can retain the ability to differentiate into multiple cell types without propagating DNA errors. Previous studies have suggested that mechanisms of genome surveillance, including DNA repair, are superior in mouse embryonic stem cells compared with various differentiated murine cells. Using single-cell gel electrophoresis (comet assay) we found that human embryonic stem cells (BG01, I6) have more efficient repair of different types of DNA damage (generated from H2O2, UV-C, ionizing radiation, or psoralen) than human primary fibroblasts (WI-38, hs27) and, with the exception of UV-C damage, HeLa cells.

Werner protein cooperates with the XRCC4-DNA ligase IV complex in end-processing.

Werner syndrome is a rare human disease characterized by the premature onset of aging-associated pathologies, cancer predisposition, and genomic instability. The Werner protein (WRN), which is defective in Werner syndrome ( WS) patients, belongs to the RecQ family helicases and interacts with several DNA metabolic proteins, including DNA repair factors and telomere associated proteins. Nonhomologous end-joining (NHEJ) is an important pathway in the repair of DNA double strand breaks (DSBs), and the DNA-PK complex, composed of the heterodimer Ku 70/86 and the DNA-PK catalytic subunit (DNA-PKcs), together with the XRCC4-DNA ligase IV complex (X4L4), are major factors.

The human Werner syndrome protein stimulates repair of oxidative DNA base damage by the DNA glycosylase NEIL1.

The mammalian DNA glycosylase, NEIL1, specific for repair of oxidatively damaged bases in the genome via the base excision repair pathway, is activated by reactive oxygen species and prevents toxicity due to radiation. We show here that the Werner syndrome protein (WRN), a member of the RecQ family of DNA helicases, associates with NEIL1 in the early damage-sensing step of base excision repair. WRN stimulates NEIL1 in excision of oxidative lesions from bubble DNA substrates.

Inhibitory effect of tramadol on vasorelaxation mediated by ATP-sensitive K+ channels in rat aorta.

Purpose: Tramadol produces a conduction block similar to lidocaine by exerting a local anesthetic-like effect. The aims of this in vitro study were to determine the effects of tramadol on the vasorelaxant response induced by the adenosine triphosphate-sensitive K(+) (K(ATP)) channel opener, levcromakalim, in an endothelium-denuded rat aorta, and to determine whether this effect of tramadol is stereoselective.

Methods: The effects of tramadol (racemic, R(-) and S(+): 10(-6), 10(-5), 5 x 10(-5) M), and glibenclamide on the levcromakalim dose-response curve were assessed in aortic rings that had been pre-contracted with phenylephrine.

Modulation of Werner syndrome protein function by a single mutation in the conserved RecQ domain.

Naturally occurring mutations in the human RECQ3 gene result in truncated Werner protein (WRN) and manifest as a rare premature aging disorder, Werner syndrome. Cellular and biochemical studies suggest a multifaceted role of WRN in DNA replication, DNA repair, recombination, and telomere maintenance. The RecQ C-terminal (RQC) domain of WRN was determined previously to be the major site of interaction for DNA and proteins.

Physical and functional mapping of the replication protein a interaction domain of the werner and bloom syndrome helicases.

The single-stranded DNA-binding protein replication protein A (RPA) interacts with several human RecQ DNA helicases that have important roles in maintaining genomic stability; however, the mechanism for RPA stimulation of DNA unwinding is not well understood. To map regions of Werner syndrome helicase (WRN) that interact with RPA, yeast two-hybrid studies, WRN affinity pull-down experiments and enzyme-linked immunosorbent assays with purified recombinant WRN protein fragments were performed. The results indicated that WRN has two RPA binding sites, a high affinity N-terminal site, and a lower affinity C-terminal site.

Deficiency in 3'-phosphoglycolate processing in human cells with a hereditary mutation in tyrosyl-DNA phosphodiesterase (TDP1).

Tyrosyl-DNA phosphodiesterase (TDP1) is a DNA repair enzyme that removes peptide fragments linked through tyrosine to the 3' end of DNA, and can also remove 3'-phosphoglycolates (PGs) formed by free radical-mediated DNA cleavage. To assess whether TDP1 is primarily responsible for PG removal during in vitro end joining of DNA double-strand breaks (DSBs), whole-cell extracts were prepared from lymphoblastoid cells derived either from spinocerebellar ataxia with axonal neuropathy (SCAN1) patients, who have an inactivating mutation in the active site of TDP1, or from closely matched normal controls. Whereas extracts from normal cells catalyzed conversion of 3'-PG termini, both on single-strand oligomers and on 3' overhangs of DSBs, to 3'-phosphate termini, extracts of SCAN1 cells did not process either substrate.

Pathways and functions of the Werner syndrome protein.

Mutations in human WRN (also known as RECQ3) gene give rise to a rare autosomal recessive genetic disorder, Werner syndrome (WS). WS is a premature aging disease characterized by predisposition to cancer and early onset of symptoms related to normal aging including osteoporosis, ocular cataracts, graying and loss of hair, diabetes mellitus, arteriosclerosis, and atherosclerosis. This review focuses on the functional role of Werner protein (WRN) in guarding the genetic stability of cells, particularly by playing an integral role in the base excision repair, and at the telomere ends.

DNA end sequestration by DNA-dependent protein kinase and end joining of sterically constrained substrates in whole-cell extracts.

Extracts of Xenopus eggs and of cultured human and hamster cells have the capacity to join nonhomologous DNA ends, and all do so with similar specificity. To examine the formation of repair complexes on DNA under conditions of end joining, end-labeled fragments were incubated with the various extracts and then subjected to DNase-I footprinting. Human and Xenopus extracts produced footprints virtually identical to that of purified DNA-dependent protein kinase holoenzyme (Ku plus DNA-PKcs), with protection of the terminal 28 bp.

Implication of DNA polymerase lambda in alignment-based gap filling for nonhomologous DNA end joining in human nuclear extracts.

Accurate repair of free radical-mediated DNA double-strand breaks by the nonhomologous end joining pathway requires replacement of fragmented nucleotides in the aligned ends by a gap-filling DNA polymerase. Nuclear extracts of human HeLa cells, supplemented with recombinant XRCC4-DNA ligase IV complex (XRCC4/ligase IV), were capable of accurately rejoining model double-strand break substrates with a 1- or 2-base gap, and the gap-filling step was dependent on XRCC4/ligase IV. To determine what polymerase was responsible for gap filling, end joining was examined in the presence of polyclonal antibodies against each of two prime candidate enzymes, DNA polymerases mu and lambda, both of which were present in the extracts.

Requirement for XRCC4 and DNA ligase IV in alignment-based gap filling for nonhomologous DNA end joining in vitro.

In the nonhomologous end joining pathway of DNA double-strand break repair, the ligation step is catalyzed by a complex of XRCC4 and DNA ligase IV. Extracts of CHO-K1 cells are able to accurately rejoin a site-specific free radical-mediated double-strand break with partially complementary overhangs, by a mechanism involving alignment-based gap filling followed by ligation. Extracts of XR-1 cells, which lack XRCC4 and DNA ligase IV, carried out neither gap filling nor ligation.

Gene rearrangements induced by the DNA double-strand cleaving agent neocarzinostatin: conservative non-homologous reciprocal exchanges in an otherwise stable genome.

Among a collection of 74 aprt mutations induced by treatment of plateau phase Chinese hamster ovary CHO cells with the radiomimetic DNA double-strand cleaving agent neocarzinostatin, nine were large-scale rearrangements. Molecular analysis indicated that all nine were highly conservative, non-homologous reciprocal exchanges, most of which were intrachromosomal as determined by fluorescence in situ hybridization. All but one of the parental sequences contained potential double-strand cleavage sites positioned such that the observed rearrangements could be explained by drug-induced double-strand breakage followed by trimming, templated patching and ligation of the exchanged ends.