The National Academy of Sciences of Belarus

A GEANT4-based Monte Carlo simulation model of an underwater gamma-ray spectrometer based on europium-doped strontium iodide (SrI₂(Eu)) is developed and validated in this study. The scintillator has superior properties - including excellent energy resolution (∼ 3% at 662keV), high light yield (90 photons/keV), and minimal intrinsic radioactivity - that make it particularly suitable for aquatic radiation monitoring. The GEANT4 model uses the Penelope physics list for accurate low-energy simulation. A direct comparison was made between the baseline Penelope model and the standard electromagnetic physics list (G4EmStandardPhysics). A comprehensive library of detector response functions (DRFs) was generated, covering gamma-ray energies from 50keV to 3MeV to establish the gamma-ray detection efficiency in the full operation range. Experimental validation is performed in an 8m³ water tank using calibrated radioactive solutions of ¹³⁹Ce (gamma-ray energy 165.8keV), ¹³⁷Cs (661.6keV), and ⁸⁸Y (898.0and1836.0keV), which showed excellent agreement ( 1%) with a tank-replication simulation. Another simulation, which used an energy-dependent effective volume (V_eff) to model an infinite water geometry, revealed a significant 12.5% discrepancy at 1836 keV that is attributed to finite tank volume effects.

Terminal deoxynucleotidyl transferase (TdT) is a unique DNA polymerase that catalyzes the template-independent addition of nucleotides to the 3' terminus of single-stranded DNA. Its distinctive catalytic properties have been exploited in aptasensor design, nanomaterial synthesis, DNA mutagenesis, innovative data storage based on single-nucleotide DNA sequences, and enzymatic de novo DNA synthesis. However, the application of the enzyme is limited by its low expression yield, poor thermostability, and reduced nucleotide incorporation efficiency with substrates prone to forming secondary structures. To overcome these limitations, we engineered a bovine TdT variant truncated at the N-terminus by 148 residues (148_TrTdT), which demonstrates a twofold increase in expression yield, a 5 °C improvement in thermostability, and over 30 % enhancement in nucleotide incorporation efficiency and processivity compared to the wild-type enzyme. Moreover, we demonstrated that DNA-binding proteins enhance the nucleotide incorporation activity of native TdT (10-fold) and 148_TrTdT (2-fold) when substrates are prone to forming secondary structures. Collectively, the methodologies implemented in this study exhibit significant potential for enhancing the efficiency of enzymatic de novo DNA synthesis, thereby enabling the development of new bioengineering and biomedical applications.

The base editor (BE) and prime editing guide RNA (pegRNA)-based prime editor (PE) technologies relying on the CRISPR/Cas system are very efficient gene editors that have been developed in recent years. The BEs include cytosine base editors (CBEs) that mediate the conversion of C to T, adenine base editors (ABEs) that mediate the conversion of A to G, glycosylase base editors (GBEs) that mediate the conversion of C to G, and the dual-base editors (DBEs) that mediate the simultaneous conversion of C to T and A to G. The BEs and PEs have been successfully applied for genome editing of various animals, plants, and microorganisms due to their advantages of high efficiency and independence of DNA double-strand breaks or donor DNA. The development process and characteristics of various BEs and PEs and their effectiveness of application are systematically introduced to provide a reference for selecting appropriate genome editing technologies. Moreover, the urgent issues that need to be addressed for more efficient and precise editing are summarized and prospected.