Guanosine-5'-diphosphate 3'-diphosphate (ppGpp) serves as alarmone in bacterial stringent responses. In this study, an affinity column was constructed by immobilizing ppGpp to NHS-Sepharose for isolating ppGppbinding proteins. A novel ppGpp-binding protein, YjgA, was isolated and characterized by MALDI-TOF MS (matrix-assisted laser desorption ionization-time-of-flight mass spectrometry) coupled with two-dimensional gel electrophoresis. YjgA and truncated forms of YjgA were cloned and over-expressed in BL21 (DE3). The binding affinity of YjgA to ppGpp was determined by equilibrium dialysis. The interaction of YjgA with ppGpp was very specific, considering that the dissociation constant of YjgA with ppGpp was measured as 5.2 ± 2.0 µM, while the affinities to GTP and GDP were about 60 and 30 times weaker than ppGpp. Expression of yjgA gene in Escherichia coli K-12 MG1655 was examined by reverse transcription polymerase chain reaction (RT-PCR). RT-PCR results revealed that yjgA was expressed from early to late stationary phase. The yjgA deletion mutant exhibited decreased cell number at stationary phase compared to parent strain and the overexpression of YjgA increased the cell number. These results suggested that YjgA might stimulate cell division under stationary phase. In most prokaryotic genome, about half of the protein candidates are hypothetical, that are expected to be expressed but there is no experimental report on their functions. The approach utilized in this study may serve as an effective mean to probe the functions of hypothetical proteins.
Optical signals necessitate using filters that selectively transmit or reflect light with the desired wavelength information. In visual imaging‐related devices, a color filter acts as a wavelength selector to extract certain information from the incident light. To overcome the limitations of commercial pigmented color filters, structural color filters with controllable photonic bandgaps (PBGs) have recently attracted significant interest. Especially, chiral liquid crystal (CLC) has been widely investigated for tunable color filters owing to its selective reflection. However, most of the research has been limited to the control of conventional reflection rather than transmission wavelength. This study proposes an electrically wavelength‐tunable color filter with high optical transmittance using a heterogeneous CLC with extremely small voltages not exceeding 1.4 V. Electrothermal tuning of CLC is approached so that transmission wavelength of the device can be tuned among red, green, and blue. Moreover, analog pixel binning using CLC color filters is explored in a tetra‐layout beyond state‐of‐the‐art pixel binning with post‐capture digital image processing. Dynamic and direct binning can prevent the quality degradation of the images captured under low‐light illumination in image sensors. The wavelength‐tunable transmission color filter proposed in this study is expected to facilitate future electro‐optical dynamic color filter applications.
Optical signals necessitate using optical filters that selectively transmit light with the desired wavelength information. In visual imaging-related optical devices, a color filter acts as an optical wavelength selector to extract the certain color information from the incident light. To overcome the optical limitations of the conventionally commercialized pigmented color filters, such as low efficiency and low color purity, biomimetic structural color filters have recently attracted significant interest. Chiral liquid crystals form a self-organized periodic helical nanostructure and the implemented structural color can be tunable. However, most of chiral liquid crystal color and control of filtered color wavelength have been limited to the reflection rather than optically transmissive color filters. This study proposes an electrically tunable color filter using a heterogeneous chiral liquid crystal structure whose transmissive light can be tuned among different colors (red, green, and blue) with extremely small voltages not exceeding 1.2 V for the first time to the best of our knowledge. To obtain electrical controllability of transmissive colors, electrothermal tuning of chiral liquid crystals is approached. Moreover, analog pixel binning with a heterogeneous chiral liquid crystal color filter in a tetra-layout is investigated. Dynamic and direct binning of the color filter could relieve the quality degradation of the captured images under low-light illumination in image sensors and higher image resolutions. Considering the highly desired requirement of low driving voltage in practical devices, the tunable heterogeneous CLC color filter proposed in this study is expected to facilitate the advancement of future electro-optical color filter applications.
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