Structural mimicry confers robustness in the cyanobacterial circadian clock

The histidine kinase SasA enhances robustness of circadian rhythms in the cyanobacterium S. elongatus by temporally controlling expression of the core clock components, kaiB and kaiC. Here we show that SasA also engages directly with KaiB and KaiC proteins to regulate the period and enhance robustness of the reconstituted circadian oscillator in vitro, particularly under limiting concentrations of KaiB. In contrast to its role regulating gene expression, oscillator function does not require SasA kinase activity; rather, SasA uses structural mimicry to cooperatively recruit the rare, fold-switched conformation of KaiB to the KaiC hexamer to form the nighttime repressive complex. Cooperativity gives way to competition with increasing concentrations of SasA to define a dynamic window by which SasA directly modulates clock robustness.One Sentence SummarySasA controls the assembly of clock protein complexes through a balance of cooperative and competitive interactions.

Mecanismo Diseñado y Simulado Virtualmente

Objectives: To show a process to synthesize and analyze a crank mechanism oscillator function generator. Simulate it in a virtual reality environment, without losing its physical characteristic. Evaluate deviations between analytically desired and virtually obtained. Methodology: Using the analytical method described by Hartenberg and Denavit, a graphic package and an electronic spreadsheet; knowing the angle of rotation of the crank, the angular reference position of the crank, the displacement of the oscillator, the extreme values of the independent variable and the function; precision positions, link lengths, eccentricity and oscillator reference position were determined. The links were generated, the mechanism was assembled, analyzing fifteen of its positions. Of the infinite number of existing solutions, five were synthesized. For each solution that justify it, the deviation of the generated function was evaluated with respect to the desired one. Contribution: The friendly, fast, safe, accurate and parametric process was demonstrated; modifying the inputs and checking the update of the outputs, therefore it is a contribution to the scientific progress of the area.

Photoperiod sensing of the circadian clock is controlled by EARLY FLOWERING 3 and GIGANTEA

SummaryELF3 and GI are two important components of the Arabidopsis circadian clock. They are not only essential for the oscillator function but are also pivotal in mediating light inputs to the oscillator. Lack of either results in a defective oscillator causing severely compromised output pathways, such as photoperiodic flowering and hypocotyl elongation. Although single loss of function mutants of ELF3 and GI have been well-studied, their genetic interaction remains unclear. We generated an elf3 gi double mutant to study their genetic relationship in clock-controlled growth and phase transition phenotypes. We found that ELF3 and GI repress growth differentially during the night and the day, respectively. Circadian clock assays revealed that ELF3 and GI are essential Zeitnehmers that enable the oscillator to synchronize the endogenous cellular mechanisms to external environmental signals. In their absence, the circadian oscillator fails to synchronize to the light-dark cycles even under diurnal conditions. Consequently, clock-mediated photoperiod-responsive growth and development is completely lost in plants lacking both genes, suggesting that ELF3 and GI together convey photoperiod sensing to the central oscillator. Since ELF3 and GI are conserved across flowering plants and represent important breeding and domestication targets, our data highlight the possibility of developing photoperiod-insensitive crops by adjusting the allelic combination of these two key genes.One sentence summaryELF3 and GI are essential for circadian clock mediated photoperiod sensing.

An Overview of Charge Pump for Phase Lock Loop System for High Frequency Application.

Phase lock loop is fundamental buliding block of modern communication system. Phase lock loop are typically used to provide local oscillator function in radio reciver or transmitter. The design methodology and test result of charge pump structure for phase lock loop application are presented. The structure is composed to two charge/ discharge block. This paper provides study of various charge pump and discuss the technology that is used to design charge pump.

An Overview of Charge Pump for Phase Lock Loop System for High Frequency Application

Phase lock loop is fundamental building block of modern communication system. Phase lock loop are typically used to provide local oscillator function in radio receiver or transmitter. The design methodology and test result of charge pump structure for phase lock loop application are presented. The structure is composed of two charge / discharge block. This paper provides study of various charge pump and discuss the technologies that is used to design charge pump.

Convolution Models for the Dielectric Function of Glass

Spectral behaviour of the real and imaginary parts of the optical constants of glass has been widely investigated to obtain band structural parameters of optically induced transitions. Curve fitting procedures for obtaining a classical oscillator fit to reflectance and/or transmittance data play an important role in this application. The present form of the dispersion model that is widely used to describe disordered media like glass uses a convolution of the Lorentzian oscillator function and the Gaussian Probability Density Function. This model is capable of describing symmetrical band shapes only. In this paper a convolution model is proposed based on using the Beta function as PDF. The maximum of the PDF, which corresponds to the frequency with the highest probability, corresponds to the central frequency of the particular oscillator species in the convolution model. For a certain value of the parameter that describes the degree of asymmetry, the new model is equivalent with the present convolution model and the remaining parameters have an identical meaning yielding practically identical values. The new model also solves a problem related to the infinite integration intervals of the Gaussian PDF based convolution model.