6,886 research outputs found
Sequential multiple functions of the conserved sequence in sequence-specific termination by T7 RNA polymerase
No full texthttp://www.pnas.org/cgi/content/abstract/102/1/75?ctEscherichia coli rrnB terminator t1 contains an RNA hairpin-dependent (class I) and a sequence-specific (class II) termination signal. The latter consists of an 8-bp conserved sequence (CS), TATCTGTT, immediately followed by an 8-bp T rich sequence. In this study, elongation complexes of T7 RNA polymerase at various positions of the class II signal and several mutant signals were obtained by stepwise walking on immobilized DNA templates free of the class I signal. Multiple CS-associated conformational changes were observed, starting at the beginning of the signal and occurring sequentially. When the complexes reach the first base pair of the CS-DNA duplex, which is downstream of the RNA-DNA heteroduplex, their stability, as measured by time-course retention of radiolabeled transcripts, markedly decreases. Further elongation leads to an abrupt change in polymerase-RNA interaction. Crosslinking of the polymerase to a 4-thio-UMP incorporated into RNA 8 nucleotides upstream of the 3' end and just upstream of the heteroduplex is initially strong but diminishes when the polymerase reaches the fourth base pair of the CS. After a further 7-nt elongation, the exposed single-stranded region of nontemplate strand is contracted; RNA in the upstream half of the heteroduplex becomes dissociated, and the CS-DNA duplex is reformed. During the next 5-nt elongation before termination, the CS duplex is prevented from translocation, and the contracted transcription bubble expands only downstream. These findings suggest that the CS duplex plays essential roles by successively binding to polymerase both downstream and upstream of the heteroduplex.the Korea Science and Engineering Foundation (R01-1999-00111) and the 21C Frontier Project (M1-03KB010006). Y.S. is a recipient of a postdoctoral fellowship (M02-2004-000-11191-0
ENHANCED METAL-AFFINITY PARTITIONING OF GENETICALLY-ENGINEERED HIRUDIN VARIANTS IN POLYETHYLENE-GLYCOL DEXTRAN 2-PHASE SYSTEMS
No full textHirudin variants were constructed to exhibit an increased metal-binding affinity in an attempt to apply a metal-affinity partitioning process in a primary separation step for purification of hirudin. The hirudin variants were genetically engineered to contain additional surface-accessible histidines and produced by recombinant Saccharomyces cerevisiae. The partitioning behavior of these variants was compared with that of the wild type with a single surface-accessible histidine at position 51. Upon the addition of a small amount of Cu(II)IDA-PEG (Cu(II)iminodiacetic acid-polyethylene glycol) ligand to PEG/dextran two-phase systems, the hirudin variants with two or three surface-accessible histidines were more selectively partitioned into the PEG-rich phase than the wild type. Integrating protein engineering to metal-affinity partitioning offers the potential for general application of this technique to facilitate protein isolation, but the genetically engineered protein variants should be carefully constructed in a manner to minimize reduction of native protein activity
HIGH RESOLUTION FOURIER TRANSFORM EMISSION SPECTROSCOPY OF YH AND YD.
No full textAuthor Institution: Department of Chemistry, University of Arizona; Department of Chemistry, University of WaterlooThe electronic emission spectrum of YH and YD has been investigated in the 690 nm to 3 spectral region using a Fourier transform spectrometer. The YH and YD bands were excited in an yttrium hollow cathode lamp operated with neon gas and a trace of of The observed bands have been classified into three different electronic transitions; and . The transition of YD could not be identified due to its very weak intensity. The rotational analysis of several bands of the transition (up to for YH and for YD) provides improved equilibrium vibrational and rotational constants for the ground state of YH and YD. The excited state is involved in several perturbations
An autonomous SRAM with on-chip sensors in an 80-nm double stacked cell technology
No full textAn active solution is proposed to overcome the uncertainty and fluctuation of the device parameters in nanotechnology SRAM. The proposed scheme is composed of sensing blocks, analysis blocks and control blocks. An on-chip timer, temperature sensor, substrate noise detector, and leakage current monitor are used to monitor internal status of chip during operation. From the sensed data, internal supply voltage, internal timing margin from decoding to sensing time, substrate noise from digital area, and low voltage level of wordline are controlled. A 512-kb test SRAM chip, fabricated with an 80-nm double stacked cell technology, shows that average power consumption is reduced by 9% and the standard deviation decreases by 58%
Low-power 3D graphics processors for mobile terminals
No full textA full 3D graphics pipeline is investigated, and optimizations of graphics architecture are assessed for satisfying the performance requirements and overcoming the limited system resources found in mobile terminals. Two mobile 3D graphics processor architectures, RAMP and DigiAcc, are proposed based on the analysis, and a prototype development platform (REMY) is implemented. REMY includes a software graphics library and simulation environment developed for more flexible realization of mobile 3D graphics. The experimental results demonstrate the feasibility of mobile 3D graphics with 3.6 Mpolygons/s at 155 mW power consumption for full 3D operation
Radio frequency magnetron sputter-deposited indium tin oxide for use as a cathode in transparent organic light-emitting diode
No full textIndium tin oxide (ITO) films were prepared by radio frequency magnetron sputtering at room temperature, for use as a cathode in a transparent organic light-emitting diode (TOLED). To minimize damage to the TOLED by the ITO sputtering process, the target-to-substrate distance was increased to 20 cm. An ITO film deposited at the optimum oxygen partial pressure exhibited an electrical resistivity as low as 4.06 x 10(-4) ohm cm and a high optical transmittance of 91% in the visible range. The film was used as a transparent cathode for a TOLED with structure of an ITO coated glass substrate /Naphthylphenyldiamide (60 nm)/Tris-(8-hydroxyquinoline) aluminum (60 nm)/LiF (1 nm)/Al (2 nm)/Ag (8 nm)/ITO cathode (100 nm). A maximum luminance of 37,000 cd/m(2) was obtained. The device performance was comparable to a conventional OLED. (c) 2005 Elsevier B.V All rights reserved
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