Random mutagenesis and selection of Escherichia coli cytosine deaminase for cancer gene therapy

Cytosine deaminase (CD) is currently being used as a suicide gene for cancer gene therapy. The premise of this therapy is the preferential deamination of 5-fluorocytosine (5FC) to 5-fluorouracil by cancer cells expressing cytosine deaminase. However, a lack of efficient gene transfer to tumors combined with inefficient 5FC turnover currently limits the clinical applications of this gene therapy approach. We have used random mutagenesis to create novel bacterial cytosine deaminases that demonstrate an increased preference for 5FC over cytosine. Among the 15 mutants isolated, one conferred sensitivity to Escherichia coli in a negative selection system at a concentration of 5FC that was 10-fold lower than a sublethal dose for wild-type CD. Evaluation of individual substitutions found in this double mutant (Q102R, D314G) demonstrated that the substitution at residue D314 was solely responsible for the observed increase in sensitivity to 5FC. Additional mutagenesis at D314 resulted in the identification of two more substitutions with the ability to confer enhanced 5FC sensitivity to E.coli. Structure determinations of the three CD variants in the presence and absence of a transition state 5FC analogue provide insights to the determinants of substrate binding specificity at the 5' position of the pyrimidine ring. CD mutant D314A is a promising candidate for further gene therapy studies.     

Characterization of HgCdTe Films Grown on Large-Area CdZnTe Substrates by Molecular Beam Epitaxy

Recent advances in growth of Hg_1?x Cd _x Te films on large-area (7 cm × 7.5 cm) CdZnTe (CZT) substrates is presented. Growth of Hg_1?x Cd _x Te with good uniformity on large-area wafers is achieved using a Riber 412 molecular beam epitaxy (MBE) tool designed for growth of Hg_1?x Cd _x Te compounds. The reactor is equipped with conventional CdTe, Te, and Hg sources for achieving uniform exposure of the wafer during growth. The composition of the Hg_1?x Cd _x Te compound is controlled in situ by employing a closed-loop spectral ellipsometry technique to achieve a cutoff wavelength (λ _co) of 14 μm at 78 K. We present data on the thickness and composition uniformity of films grown for large-format focal-plane array applications. The composition and thickness nonuniformity are determined to be <1% over the area of a 7 cm × 7.5 cm wafer. The films are further characterized by Fourier-transform infrared spectroscopy, optical microscopy, and Hall measurements. Additionally, defect maps show the spatial distribution of defects generated during the epitaxial growth of the Hg_1?x Cd _x Te films. Microdefect densities are in the low 10³ cm^?2 range, and void defects are below 500 cm^?2. Dislocation densities less than 5 × 10⁵ cm^?2 are routinely achieved for Hg_1?x Cd _x Te films grown on CZT substrates. HgCdTe 4k × 4k focal-plane arrays with 15 μm pitch for astronomical wide-area infrared imagers have been produced using the recently developed MBE growth process at Teledyne Imaging Sensors.     

石英陶瓷材料的研制

采用废石英玻璃制备了石英陶瓷材料，讨论了石英玻璃粒度和烧结温度对材料性能的影响，借助于XRD测试手段分析其物相组成。结果表明：具有合理的粒度级配，在1300℃温度下烧成可制得主晶相为α-方石英，晶粒粒度为50-110nm，并含有一定量的玻璃相，性能较为理想的石英陶瓷材料。     

A Report on Mudd Design Workshop II: “Designing Design Education for the 21st Century”

This paper reports on a workshop on design education held at Harvey Mudd College (HMC) in May 1999. Mudd Design Workshop II was intended to provide a forum that would bring together design educators, design researchers, and designers from industry, in order to focus exclusively on the teaching of design in engineering education for the next century. Sessions were devoted to (1) design projects in both cornerstone and capstone courses, and metrics for selecting projects; (2) discipline‐based and cross‐disciplinary design courses; and (3) pedagogy, technology, and assessment in design education. Major emergent themes included the desirability of design throughout the curriculum, focuses on coaching and on learning, roles of projects and interactive learning, and the need to better address the interactions of grading and learning. Participants' specific commitments to future actions are also given.     

Engaging student diversity through a Social Justice Learning Community.

Liberal arts institutions are unique in their emphasis on learning and social environments that value diverse interpersonal and intergroup relationships. This case study examines the institutionalization of a faculty-initiated program—the Social Justice Learning Community (SJLC)—at an historically White liberal arts college for women that recently experienced significant change in the race, class, and sexual orientation of its student body. The SJLC served as a curricular response to the tensions surrounding diversity and as a tool for crafting an inclusive institutional identity through its use of a critical multicultural framework grounded in dialogue and social engagement and its strategy of linking institutional mission to programmatic goals to insure sustainability and viability within the institutional structure. We use a framework of phased institutionalization to explore how the SJLC changed and challenged institutional responses to and engagement of diversity on campus. The study poses the following research questions: (1) What were the structures and processes used by the SJLC to respond to student diversity? and (2) How has the implementation of these structures and processes influenced a phased institutionalization of the SJLC as an effective diversity initiative? Our work is supported with the insights of two study participants who served as founding members and as past directors for the SJLC and offers a model of how committed attention to diversity by faculty, staff, and students utilizing a critical multicultural framework as an organizing principle supports the building of a multicultural campus community. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Randomized controlled trial of motivational enhancement therapy with nontreatment-seeking adolescent cannabis users: A further test of the teen marijuana check-up.

Cannabis use adversely affects adolescents and interventions that are attractive to adolescents are needed. This trial compared the effects of a brief motivational intervention for cannabis use with a brief educational feedback control and a no-assessment control. Participants were randomized into one of three treatment conditions: Motivational Enhancement Therapy (MET), Educational Feedback Control (EFC), or Delayed Feedback Control (DFC). Those who were assigned to MET and EFC were administered a computerized baseline assessment immediately following randomization and completed assessments at the 3- and 12-month follow-up periods. Participants in the DFC condition were not assessed until the 3-month follow-up. Following the completion of treatment sessions, all participants were offered up to four optional individual treatment sessions aimed at cessation of cannabis use. The research was conducted in high schools in Seattle, Washington. The participant s included 310 self-referred adolescents who smoked cannabis regularly. The main outcome measures included days of cannabis use, associated negative consequences, and engagement in additional treatment. At the 3-month follow-up, participants in both the MET and EFC conditions reported significantly fewer days of cannabis use and negative consequences compared to those in the DFC. The frequency of cannabis use was less in MET relative to EFC at 3 months, but it did not translate to differences in negative consequences. Reductions in use and problems were sustained at 12 months, but there were no differences between MET and EFC interventions. Engagement in additional treatment was minimal and did not differ by condition. Brief interventions can attract adolescent cannabis users and have positive impacts on them, but the mechanisms of the effects are yet to be identified. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The importance of the trans-enamine intermediate as a β-lactamase inhibition strategy probed in inhibitor-resistant SHV β-lactamase variants

The ability of bacteria to express inhibitor‐resistant (IR) β‐lactamases is stimulating the development of novel inhibitors of these enzymes. The 2′β‐glutaroxypenicillinate sulfone, SA2‐13, was previously designed to enhance the stabilization of the deacylation‐refractory, trans‐enamine inhibitory intermediate. To test whether this mode of inhibition can overcome different IR mutations, we determined the binding mode of SA2‐13 through X‐ray crystallography, obtaining co‐crystals of the inhibitor–protein complex by soaking crystals of the IR sulfhydryl variable (SHV) β‐lactamase variants S130G and M69V with the inhibitor. The 1.45 Å crystal structure of the S130G SHV:SA2‐13 complex reveals that SA2‐13 is still able to form the stable trans‐enamine intermediate similar to the wild‐type complex structure, yet with its carboxyl linker shifted deeper into the active site in the space vacated by the S130G mutation. In contrast, data from crystals of the M69V SHV:SA2‐13 complex at 1.3 Å did not reveal clear inhibitor density indicating that this IR variant disfavors the trans‐enamine conformation, likely due to a subtle shift in A237.     

Context-dependent modulation by D? receptors: Differential effects in hippocampus and striatum.

Place-specific firing by hippocampal and striatal neurons was recorded simultaneously following injection of a D? receptor antagonist (SCH23390) and during spatial working memory task performance. SCH23390-induced changes in unit responses were observed during light and dark test conditions. Although hippocampal place field locations were altered by the contextual change, the reliability and specificity of place fields was disrupted only by combining D? antagonism and a change in context. Striatal place field locations were reorganized after either contextual change or D? antagonism, without altering place field reliability and specificity. Disrupted velocity encoding by place cells in both regions was induced by darkness, whereas greater stability in acceleration encoding followed removal of D? receptor activity. Dopamine may differentially regulate hippocampal context learning and striatum-based predictive codes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)