Allosteric Regulation of Recombination Enzymes \u3cem\u3eE. coli\u3c/em\u3e RecA and Human Rad51: A Dissertation

ATP plays a critical role in the regulation of many enzyme processes. In this work, I have focused on the ATP mediated regulation of the recombination processes catalyzed by the E. coliRecA and the human Rad51 proteins. The RecA protein is a multifunctional enzyme, which plays a central role in the processes of recombinational DNA repair, homologous genetic recombination and in the activation of the cellular SOS response to DNA damage. Each of these functions requires a common activating step, which is the formation of a RecA-ATP-ssDNA nucleoprotein filament. The binding of ATP results in the induction of a cooperative, high affinity ssDNA binding state within RecA (Menetski & Kowalczykowski, 1985b; Silver & Fersht, 1982). Data presented here identifies Gln194 as the NTP binding site γ-phosphate sensor , in that mutations introduced at this residue disrupt all ATP induced RecA activities, while basal enzyme function is maintained. Additionally, we have dissected the parameters contributing to cooperative nucleoprotein filament assembly in the presence of cofactor. We show that the dramatic increase in the affinity of RecA for ssDNA in the presence of ATP is a result of a significant increase in the cooperative nature of filament assembly and not an increase in the intrinsic affinity of a RecA monomer for ssDNA. Previous work using both mutagenesis and engineered disulfides to study the subunit interface of the RecA protein has demonstrated the importance of Phe217 for the maintenance of both the structural and functional properties of the protein (Skiba & Knight, 1994; Logan et al., 1997; Skiba et al., 1999). A Phe217Tyr mutation results in a striking increase in cooperative filament assembly. In this work, we identify Phe217 as a key residue within the subunit interface and clearly show that Phe217 is required for the transmission of ATP mediated allosteric information throughout the RecA nucleoprotein filament. The human Rad51 (hRad51) protein, like its bacterial homolog RecA, catalyzes genetic recombination between homologous single and double stranded DNA substrates. This suggests that the overall process of homologous recombination may be conserved from bacteria to humans. Using IAsys biosensor technology, we examined the effect of ATP on the binding of hRad51 to ssDNA. Unlike RecA, we show that hRad51 binds cooperatively and with high affinity to ssDNA both in the presence and absence of nucleotide cofactor. These results show that ATP plays a fundamentally different role in hRad51 vs.RecA mediated processes. In summary, through the work presented in this dissertation, we have defined the critical molecular determinants for ATP mediated allosteric regulation within RecA. Furthermore, we have shown that ATP is not utilized by Rad51 in the same manner as shown for RecA, clearly defining a profound mechanistic difference between the two proteins. Future studies will define the requirement for ATP in hRad51 mediated processes

LEP and radiative electroweak breaking close the light gluino window

We show that the LEP lower bound on the chargino mass, in conjunction with the well motivated theoretical requirement of radiative electroweak symmetry breaking, imply an upper bound on the lightest Higgs boson mass (m_h\lsim62\GeV) in a supersymmetry breaking scenario where the gluino mass is a few GeV. Moreover, Higgs searches at LEP in the context of this model require m_h\gsim61\GeV. The remaining experimentally allowed region in the five-dimensional parameter space of this light gluino model is severely fine-tuned (with $\tan\beta=1.88-1.89$ and m_t=114.0-114.3\GeV) and cosmologically troublesome (with a neutralino relic abundance over {\it five-hundred times larger than allowed}). Modest improvements in sensitivity in LEP Higgs searches and Tevatron top-quark searches should soon exclude this theoretically disfavored model completely.Comment: 6 pages, no figures, tex (harvmac), CERN-TH.6890, CTP-TAMU-25/9

Self-steepening of light pulses

Self-steepening of light pulses due to propagation in medium with intensity-dependent index of refractio

Infrastructure Tolls in Texas: Evidence from the Borderplex

Do changes in toll rates affect pedestrian, car, and truck traffic across the bridges between El Paso and Ciudad Juarez, Mexico? As more and more attention is paid to the use of tolls as funding mechanisms for new road and infrastructure construction in Texas, the answer to this question has policy implications not only for local and state lawmakers, but also for firms importing and exporting goods between Texas and Mexico. This article uses bridge traffic data from the Borderplex to examine the relative impact of tolls and concludes that local policymakers have more leeway than they thought in raising funds to make infrastructure improvements.Tolls; International Bridges; Border Economics

Implementing Quantum Gates by Optimal Control with Doubly Exponential Convergence

We introduce a novel algorithm for the task of coherently controlling a quantum mechanical system to implement any chosen unitary dynamics. It performs faster than existing state of the art methods by one to three orders of magnitude (depending on which one we compare to), particularly for quantum information processing purposes. This substantially enhances the ability to both study the control capabilities of physical systems within their coherence times, and constrain solutions for control tasks to lie within experimentally feasible regions. Natural extensions of the algorithm are also discussed.Comment: 4+2 figures; to appear in PR

Task 6 storable propellant module environmental control technology Summary report

Thermal control concepts for space storable fluorine hydrazine propulsion modul

Is 8:30 a.m. Still Too Early to Start School? A 10:00 a.m. School Start Time Improves Health and Performance of Students Aged 13-16.

While many studies have shown the benefits of later school starts, including better student attendance, higher test scores, and improved sleep duration, few have used starting times later than 9:00 a.m. Here we report on the implementation and impact of a 10 a.m. school start time for 13 to 16-year-old students. A 4-year observational study using a before-after-before (A-B-A) design was carried out in an English state-funded high school. School start times were changed from 8:50 a.m. in study year 0, to 10 a.m. in years 1-2, and then back to 8:50 a.m. in year 3. Measures of student health (absence due to illness) and academic performance (national examination results) were used for all students. Implementing a 10 a.m. start saw a decrease in student illness after 2 years of over 50% (p < 0.0005 and effect size: Cohen's d = 1.07), and reverting to an 8:50 a.m. start reversed this improvement, leading to an increase of 30% in student illness (p < 0.0005 and Cohen's d = 0.47). The 10:00 a.m. start was associated with a 12% increase in the value-added number of students making good academic progress (in standard national examinations) that was significant (<0.0005) and equivalent to 20% of the national benchmark. These results show that changing to a 10:00 a.m. high school start time can greatly reduce illness and improve academic performance. Implementing school start times later than 8:30 a.m., which may address the circadian delay in adolescents' sleep rhythms more effectively for evening chronotypes, appears to have few costs and substantial benefits

Interviewer Variation in Third Party Presence During Face-to-Face Interviews

The presence of a third person in face-to-face interviews constitutes an important contextual factor that affects the interviewee\u27s responses to culturally sensitive questions (Aquilino, 1997; Casterline and Chidambaram, 1984; Mneimneh et al., 2015; Pollner and Adams, 1994). Interviewers play an essential role in requesting, achieving, and reporting on the private setting of the interview. Our recent work has shown that the rate of interview privacy varies significantly across interviewers; while some interviewers report high rates of privacy among their interviews, others report low rates of privacy for the interviews they administered (Mneimneh et al., 2018). Yet, there is a lack of understanding of what explains such interviewer variation in interview privacy. Do certain interviewer characteristics such as experience, socio-demographics, and attitudes towards privacy explain such variations? What about the measurement quality of the privacy observation measures interviewers collect? Is it possible that section-specific measures (where the interviewer collects such observations right after questionnaire sections) show less interviewer variation than end-of-the-interview measures (the commonly used method of collecting interview privacy data) because of potential differential recall across interviewers? This paper explores these research questions for the first time using data from a national mental health survey conducted in the Kingdom of Saudi Arabia. A total of 4000 face-to-face interviews were completed using a computer assisted personal interviewing (CAPI) mode. Interviewers were required to record their observations regarding the presence of a third person at the end of several questionnaire sections throughout the interview, in addition to recording this information about the overall presence of a third person at the conclusion of the interview. We use these two types of observations and measure the contribution of interviewer variation to these estimates. We then compare predictors of interview privacy for each of the two types of observations using a series of multilevel models focusing on the effect of interviewer-level characteristics (while controlling for respondent and household level characteristics). Findings from this paper will have important practical implications related to training interviewers on requesting, maintaining, and reporting information on the private setting of the interview

Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms

Optical nonlocalities are elusive and hardly observable in traditional plasmonic materials like noble and alkali metals. Here we report experimental observation of viscoelastic nonlocalities in the infrared optical response of doped cadmium-oxide, epsilon-near-zero nanofilms. The nonlocality is detectable thanks to the low damping rate of conduction electrons and the virtual absence of interband transitions at infrared wavelengths. We describe the motion of conduction electrons using a hydrodynamic model for a viscoelastic fluid, and find excellent agreement with experimental results. The electrons elasticity blue-shifts the infrared plasmonic resonance associated with the main epsilon-near-zero mode, and triggers the onset of higher-order resonances due to the excitation of electron-pressure modes above the bulk plasma frequency. We also provide evidence of the existence of nonlocal damping, i.e., viscosity, in the motion of optically-excited conduction electrons using a combination of spectroscopic ellipsometry data and predictions based on the viscoelastic hydrodynamic model.Comment: 19 pages, 5 figure

Simulating Dynamical Features of Escape Panic

One of the most disastrous forms of collective human behaviour is the kind of crowd stampede induced by panic, often leading to fatalities as people are crushed or trampled. Sometimes this behaviour is triggered in life-threatening situations such as fires in crowded buildings; at other times, stampedes can arise from the rush for seats or seemingly without causes. Tragic examples within recent months include the panics in Harare, Zimbabwe, and at the Roskilde rock concert in Denmark. Although engineers are finding ways to alleviate the scale of such disasters, their frequency seems to be increasing with the number and size of mass events. Yet, systematic studies of panic behaviour, and quantitative theories capable of predicting such crowd dynamics, are rare. Here we show that simulations based on a model of pedestrian behaviour can provide valuable insights into the mechanisms of and preconditions for panic and jamming by incoordination. Our results suggest practical ways of minimising the harmful consequences of such events and the existence of an optimal escape strategy, corresponding to a suitable mixture of individualistic and collective behaviour.Comment: For related information see http://angel.elte.hu/~panic, http://www.helbing.org, http://angel.elte.hu/~fij, and http://angel.elte.hu/~vicse