Pause Interval Research Articles

Dynamics of DNA Supercoil Relaxation by Type II Topoisomerases

Dynamics of DNA supercoil relaxation by type II topoisomerasesQing Shao∗, Laura Finzi∗, and David Dunlap#Dept. of Physics∗ and Cell Biology#, Emory University, Atlanta, GA 30322Type II topoisomerases are some of the main targets of anti-cancer drugs, since they catalyze DNA decatenation and unwinding which is crucial for cell division. A recent crystal structure shows that, during the catalytic cycle, a yeast type II topoisomerase can bend a 34 base pair DNA segment by up to 150 degrees. Bacterial gyrase, another type II topoisomerase, can wrap an approximately 100 bp DNA segment into a tight 180 degree turn. By substituting diaminopurine (DAP) deoxyribonucleotides for dATP in PCR reactions, completely triply hydrogen-bonded DNA fragments have been produced and found to be stiffer than normal DNA. These and normal DNA fragments were used as substrates for observations of topoisomerase II-mediated relaxation of plectonemes introduced in single molecules using magnetic tweezers. Observations at several ATP concentrations revealed bursts of stepwise events separated by pauses. Michaelis-Menten fitting of the data for both recombinant human topoisomerase II alpha and E. coli gyrase showed that Vmax and Km both decrease in DAP-substituted with respect to normal DNA. However, while the characteristic pause interval increased for human topoisomerase II alpha operating on DAP-substituted with respect to normal DNA, it was unchanged for E. coli gyrase. These dynamic measurements not only support the hypothesis that the strand passage reaction involves DNA bending but also suggest that DNA bending and subsequent steps in the catalytic cycle, perhaps involving ATP hydrolysis, are more efficiently coupled in gyrase than in human topoisomerase II alpha.

CSPE Best Abstract Award Session

CSPE Best Abstract Award Session

Genotype-Specific Onset of Arrhythmias in Congenital Long-QT Syndrome

The identification of the molecular-genetic substrate underlying the various forms of the congenital long-QT syndrome (LQTS) has sparked studies into possible genotype-phenotype correlations with the aim of developing genotype-tailored therapy. The onset of torsade de pointes (TdP) may differ among LQTS patients, being pause dependent in some but not all. This disparity may point to different arrhythmia mechanisms and may affect therapy strategies. We studied whether the proportion of pause-dependent TdP onset varies among LQTS genotypes. We studied all LQT1 (n=10), LQT2 (n=34), and LQT3 (n=6) patients from 4 centers for whom ECGs of TdP onset were available and analyzed whether pauses preceded TdP onset (first available ECG per patient). Pauses preceded TdP significantly more often in LQT2 (68%) than in LQT1 (0%), and the interval immediately before TdP (pause interval) was significantly longer in LQT2 than in LQT1. The proportion of pause dependence in LQT3 (33%) appeared intermediate, but this group was too small for statistical analysis. Pause dependence of TdP onset is predominant in LQT2 but absent or rare in LQT1. It is suggested that disparities in pause dependence of TdP onset may reflect different arrhythmia mechanisms.

P4-67: Circular mapping and PV isolation of the antrum by a new 32-pole foldable umbrella catheter powered by pulsed RF-energy delivery

The new ablation catheter is composed of 36 crossing single wires. If stretched, it lies close to the catheter shaft. Unfolded to an umbrella, it has a diameter of 30 mm. The crossing wires form an insulated circular network of 6 mm breadth in front of the umbrella equator allowing high resolution mapping of the intracardial tissue surface. The same wire network is used for energy delivery in pulsed mode. 18 poles each were supplied with 5 ms pulses consecutively with a pause interval of 5 ms regulated by an electronic switchbox Quadrapulse (Bard). The Medusa-Box (Bard) was chosen to distribute the energy to the electrodes. The power level of generator was set to a fix rate of 100 W. If temperature exceeded 60°C at one of the four quadrant thermistors, the ensuing RF current impulses are bypassed to an internal resistor. We examined feasibility, acute efficacy of antrum isolation of the pulmonary veins (PVI) and the safety of the procedure when first tested in humans.

Transfection of HeLa‐cells with pEGFP plasmid by impedance power‐assisted electroporation

Bioimpedance spectrometry was applied to study cell viability and pEGFP plasmid-transfection efficiency in electroporation (EP) of 20,000 HeLa cells with 0.3 microg DNA in 90 microl low conductivity 0.32 M sucrose medium of pH 7.5. Monopolar rectangular pulses, of field strength 75 V/mm, and pulse length 0.1 ms were applied in 1-16 repetitions with a 10-sec pause interval between pulses. Surviving cells were stained by crystal violet and counted using a confocal microscope. Transfected cells were fixed with 10% formaldehyde and counted as green spots in a fluorescence microscope. In the present investigation we used the method of bioimpedance spectrometry to analyze the effect of EP on survival and transfection ratio of cells in suspension. DC and low-frequency AC currents preferably pass through the medium due to the high impedance of the cell membrane. At frequencies above 10 kHz the impedance of the cell membrane starts to decrease and the impedance value of the cell suspension approach a lower limit value Rinfinity at infinite frequency. Recording of electrical impedance spectra of cells in culture was performed over a frequency range of 10 Hz to 125 kHz, allowing separation of the contribution from extracellular space and that of the cell membranes. A parallel resistance capacitance model of the cell suspension was used to evaluate the response of applying EP pulses. The values of the collective membrane resistance RM decay exponentially (r2=0.995) with the number of applied pulses. The ratio of the extrapolated value of the intact membrane resistance before pulsing, RM,0, and the value RM,N after each pulse makes an index of the effect of electroporation on the cells. The ratio RM,N/RM,0 as well as the relative change of the dissipation factor, tandelta, on the "Loss Change Index" (LCI) fits well a dose-response model (r2=0.98) with the number of applied pulses. The changes in the model parameters membrane resistance DeltaRM=[1-RM,N/RM,o] and loss factor [1-tandelta0/tandeltaN] correlate well with the transfection ratio and fraction of dead cells. Those parameters were used for power-assisted electroporation in monitoring, controlling, and optimizing the EP procedure.

Producción de carne bovina en praderas renovadas con Brachiaria brizantha cv. Marandú en el Piedemonte de los llanos Orientales de Colombia

En una finca ganadera del Piedemonte Llanero de Colombia se realizó un trabajo de recuperación de praderas de Brachiaria decumbens, degradadas por el ataque del "mión de los pastos" (Aeneolamia sp.) y con predominio de la gramínea nativa Homolepis aturensis ("paja amarga"). Los tratamientos consistieron en labranza vertical al comienzo de las lluvias, siembra de la gramínea Brachiaria brizantha cv. Marandú y de las leguminosas forrajeras Pueraria phaseoloides (Kudzú) y Arachis pintoi (maní forrajero). Además, se fertilizó con 200 kg.ha-1 de roca fosfórica y cal dolomítica, 50 kg.ha-1 de cloruro de potasio y 25 kg.ha-1 de flor de azufre. Se utilizaron 30 animales enteros o toros (sin castrar) y 30 novillos (castrados) Cebú comercial, los cuales pastorearon 15 ha de pradera mejorada y 30 ha de pradera de B. decumbens con el manejo tradicional del productor (testigo); los animales se llevaron hasta un peso al sacrificio de 460 kg/animal. En la pradera renovada la disponibilidad de forraje aumentó de 750 a2.500 kg.ha-1 MS con 28 días de descanso; el contenido de minerales y proteína también aumentó. A su vez, la carga animal en las praderas renovadas fue 1.9 veces la obtenida en las praderas con manejo tradicional. Los novillos y los toros de la pradera mejorada ganaron 233 y 270 kg.ha-1 /año más de lo que ganaron los animales de la pradera testigo. En el segundo año el ingreso neto en la pradera testigo fue de $240.000 y $146.000/ha/año para toros y novillos respectivamente, mientras que en la pradera renovada el ingreso neto correspondiente fue de $762.000 y $590.000/ha/año.

Random motility of plankton: diffusive and aggregative contributions

We examine the spatial distribution of motile zooplankton moving with a variety of idealized random motility modes. The aggregation of organisms is examined for situations where the parameters governing random motility are cued to a heterogeneous environment and vary spatially. While spatial variation in swimming speed v, always leads to aggregation, spatial variations in the duration of swimming bouts T, only leads to aggregation for some motility modes. At steady state, the concentration of organisms is proportional to 1/v and independent of τ for an organism that continually adjusts its motility in response to local conditions (random cruise motility). In comparison, an organism that sets its motility only at the start of a run (random jump motility) reaches a steady state concentration proportional to 1/(τυ 2 ). For an encounter-pause random motility, steady state concentration is proportional to [1 + (pause interval)(encounter rate)]. The latter incorporates the sensory ability and swimming behaviour exhibited by many pelagic copepods. Biodffusion is a poor descriptor of random motility as it does not distinguish between the behavioural components that bring about accumulation of organisms. Mathematical formalism is provided to link individual-based random motility to macroscale phenomenology as encapsulated in appropriate advection diffusion equations.

Stopping and restarting an unfolding action at various times.

The ability to inhibit an unfolding action is usually investigated using a stop signal (or gostop) task. The data from the stop-signal task are often described using a horse-race model whose key assumption is that each process (i.e., go, stop) exhibits stochastic independence. Using three variations of a coincident-timing task (i.e., go, gostop, and gostopgo) we extend previous considerations of stochastic independence by analysing the go latencies for prior effects of stopping. On random trials in the gostopgo task the signal sweep was paused for various times at various distances before the target. Significant increases in latency errors were reported on those trials on which the signal was paused (p <.005). Further analyses of the pause trials revealed significant effects for both the stopping interval (p <.001) and the pause interval (p <.05). Tukey post hoc analyses demonstrated increased latency errors as a linear function of the stopping interval, as expected, and decreased latency errors as a nonlinear function of the pause interval. These latter results indicate that the latencies of the go process, as reflected in the latency errors, may not exhibit stochastic independence under certain conditions. Various control mechanisms were considered in an attempt to explain these data.

Evidence of a limited visuo-motor memory used in programming wrist movements.

Human subjects can pre-program movements on the basis of visual cues. Experience in a particular task leads to the storage of appropriate control parameters which are used in programming subsequent movements, via a short-term motor memory. The form, duration and usage of this memory are, however, uncertain. Repetitive wrist flexion and extension movements were measured in four subjects. Three were neurologically normal men; the fourth subject had a peripheral large-fibre sensory neuropathy, depriving him of proprioceptive information about wrist movement. Subjects made alternating 45 degrees wrist movements between two visual targets; visual feedback of wrist position was provided for the first part of each trial. After 10 s of tracking, the subjects paused for an interval of 0-24 s before resuming tracking without visual feedback of wrist position. The positional accuracy of subsequent movements was analysed with respect to pause interval. Movement accuracy was reduced by the removal of visual feedback in all four subjects: movements after the pause interval were less accurate than those before the pause. Errors also accumulated within each sequence of movements made without visual feedback. Analysis of the first movement in each trial after the pause indicated a clear relationship between movement accuracy and pause interval. In all four subjects, movement accuracy decayed with longer pause intervals. In the deafferented subject, manipulation of the visual inputs (requiring visual fixation, rather than normal pursuit of the target; or direct viewing of the hand instead of viewing a cursor on a computer screen) affected the relationship between pause interval and subsequent movement accuracy. We propose that the memory used when producing these movements is a short-lasting visuo-motor signal, lasting a few seconds, which is derived from visual knowledge of previous movements, rather than a memory of a particular motor output. This visuo-motor signal is used to scale the amplitude of subsequent wrist movements. The brevity of the visuo-motor memory and the resultant inaccuracy of this deafferented subject and of our neurologically normal subjects implies that human feedforward control of the amplitude and position of wrist movements is severely limited.

Permanent Pacemaker Placement in Chronic Atrial Fibrillation Associated with Intermittent AV Block and Cerebral Symptoms

We examined the hypothesis that a greater than or equal to 2 second pause detected on 24-hour Holter monitoring in patients with persistent atrial fibrillation and complaints of syncope or dizziness lacked sufficient specificity to warrant implantation of a permanent pacemaker. We retrospectively reviewed cases from our 24-hour electrocardiographic (Holter) monitoring data base. A total of 411 consecutive Holter monitoring records demonstrating persistent atrial fibrillation obtained during a 5-year period (1982 to 1987) were examined. One hundred and five (26%) patients had cerebral symptoms (dizziness or syncope) as a primary indication for monitoring 80 (76%) patients were identified with documented ventricular pauses of greater than or equal to 2 seconds. Three hundred and six patients (74%) underwent 24-hour monitoring without cerebral symptoms as an indication and 209 (68%) patients had greater than or equal to 2-second pauses. Clinical information was available in 164 (50 symptomatic and 114 asymptomatic) patients. There were no significant differences in the clinical or Holter findings between the two groups. Of the 50 symptomatic patients, 15 (30%) underwent permanent pacemaker placement and the remaining 35 (70%) were managed conservatively during a mean follow-up of 23 +/- 5 months. Eleven of 15 paced (73%) and 31 of 35 (89%) nonpaced patients experienced resolution of their cerebral symptoms (NS). The sensitivity of Holter monitoring in detecting pauses of greater than or equal to 2 seconds in patients with cerebral symptoms was high (76%), but the specificity (32%) and positive predictive values (28%) were low.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral Blending in Young Children: Effects of Sound Pauses, Initial Sound, and Word Familiarity

AbstractOral blending of dictated sounds into CVC (consonant-vowel-consonant) words was markedly and significantly better when no pauses intervened between sounds than when pauses of 1 or 3 sec intervened. In Experiment 1, first graders blended better than nonreading kindergarten children, with the differences pronounced at 1 and 3 sec. In Experiment 2, kindergarten children with extensive blending and reading training blended as well as the first graders, whereas younger, beginning readers paralleled the performance of the Experiment I kindergarteners. With age held constant, the effects of training continued as the major determinant of blending. We also found interactions between pause interval and word familiarity (meaningful versus nonwords) and between word familiarity and type of initial sound (held versus stop sounds).

Speech recognition system with delayed output

In a speech recognition system of the type including a recognition unit responsive to a voice input and a conditioning input for recognizing the voice input to produce a recognition output, a start signal is produced whenever a voice input exceeds a threshold level and a pause interval detection signal is produced whenever a voice input falls below a threshold level. An output timing signal is produced when the detection signal lasts a preselected interval of time that may be either about 250 milliseconds or about 250 milliseconds plus a delay. The recognition output from the recognition unit produced in response to the detection signal is displayed in response also to the detection signal. The result is delivered to a utilization device in response to the output timing signal. The delay may be given either by a predetermined duration or an interval between those instants at which the above-mentioned 250 milliseconds have just elapsed after production of the detection signal and after production of another pause interval detection signal for a next following voice input. During the delay, it is possible either by a manually operable switch or a cancel voice input to cancel delivery of the recognition result displayed to be incorrect.

Pause Detection Thresholds in a Stop-Phoneme Environment

The minimum silent interval duration necessary to be perceived as an intrasentenee pause was investigated. The stimuli consisted of five recorded sentences within which the words “lost” and “contact” were manipulated so that their syntactic relation to one another varied in complexity from sentence to sentence. Thirty subjects, working individually, adjusted the silent interval duration between the words “lost” and “contact” to that point at which they just perceived a pause. Results indicated that complexity of syntactic structure had no effect on the obtained pause detection thresholds. Presence or absence of a plosive burst terminating the word “lost” did, however, have an effect on pause-detection thresholds. Presence of the plosive burst frequently resulted in negative pause durations, that is, the point at which the subject indicated he just detected a pause was in reality an overlap of the words “lost” and “contact.” Negative thresholds were not observed when the plosive burst was absent, thus indicating that the silent interval preceding the plosive burst may well have been perceived as part of the interword pause interval. [Supported by NIH Grant.]

Markovian models of dialogic time patterns.

THE duration histograms of pauses and vocalizations in continuous speech have the form of negative exponentials1. For example, the shortest audible pauses are most numerous and the frequency at each longer pause interval is some fixed proportion of the frequency at the next shorter interval. This implies that the probability of prolonging a given pause is constant, regardless of the elapsed time in the pause. The same holds true for duration of vocalizations. The future of the temporal sequence is then stochastically determined by the present and is independent of its history.

Social Class, Linguistic Codes and Grammatical Elements

In a previous paper (Bernstein, 1962) two general types of linguistic code, elaborated and restricted, were proposed. These codes were regarded as functions of different forms of social relationships. The codes were thought to entail qualitatively different verbal planning orientations which control different modes of self-regulation and levels of cognitive behaviour. Social class differences in the use of these codes were expected. Speech samples were obtained and the hesitation phenomena analysed, from a discussion situation involving small groups of middle and working class subjects with varying I.Q. profiles. It was found that the middle-class groups used a shorter phrase length and a longer pause interval than the working-class group. These differences in the hesitation phenomena were sharper when working-class and middle-class groups, matched for intelligence on a group verbal and non-verbal test, were compared. It was considered that the members of the two class groups were oriented to qualitatively different levels of verbal planning which control lexicon and structural selections. The working-class groups were thought to be making selections from a lower level of the linguistic hierarchy; whilst the middle-class subjects irrespective of verbal I.Q. were oriented to making selections from a higher level of the hierarchy. This paper will report the analysis of the speech.