Nucleases in gene-editing technologies:past and prologue

In recent decades,gene-editing technologies,typically based on deoxyribonucleases to specifically modify genomic sequences,have dramatically remodeled various aspects of life sciences,including fundamental research,breeding,and medical therapeutics.So far,four types of endonucleases have been adopted and optimized as gene-editing tools:meganuclease,ZFN,TALEN,and Cas nuclease from the CRISPR-Cas system.Each tool comes with its own advantages and limitations.Over the last ten years,RNA-guided Cas nucleases have been extensively investigated and successfully implemented in almost all mammalian cells due to their remarkable editing efficacy,high specificity,and flexibility in targeting the specific locus.Diverse Cas nuclease,together with meganuclease,ZFN,and TALEN,represent the key strategies for nuclease-based gene editing.However,systematic introductions and comparisons among four types of nucleases are not yet available.Here,we overview the capabilities of four types of nucleases along the development history of gene editing and describe the molecular mechanisms of substrate recognition and cleavage.Particularly,we summarize the promising CRISPR-Cas systems as well as modified tools applied for gene editing in the eukaryotic genome.Moreover,how the re-modulated nucleases and other nucleases,either naturally occurring or AI-designed,might manipulate DNA sequences is discussed and proposed.

Improved three-vector based dead-beat model predictive direct power control strategy for grid-connected inverters

Since only one inverter voltage vector is applied during each duty cycle, traditional model predictive direct power control(MPDPC) for grid-connected inverters(GCIs) results in serious harmonics in current and power. Moreover, a high sampling frequency is needed to ensure satisfactory steady-state performance, which is contradictory to its long execution time due to the iterative prediction calculations. To solve these problems, a novel dead-beat MPDPC strategy is proposed, using two active inverter voltage vectors and one zero inverter voltage vector during each duty cycle. Adoption of three inverter vectors ensures a constant switching frequency. Thus, smooth steady-state performance of both current and power can be obtained. Unlike the traditional three-vector based MPDPC strategy, the proposed three vectors are selected based on the power errors rather than the sector where the grid voltage vector is located, which ensures that the duration times of the selected vectors are positive all the time. Iterative calculations of the cost function in traditional predictive control are also removed, which makes the proposed strategy easy to implement on digital signal processors(DSPs) for industrial applications. Results of experiments based on a 1 kW inverter setup validate the feasibility of the proposed three-vector based dead-beat MPDPC strategy.