Xenolis Pte Ltd.

Engineered RNAs have applications in diverse fields from biomedical to environmental. In many cases, the folding of the RNA is critical to its function. Here we describe a strategy to improve the response time of a riboswitch-based fluorescent biosensor. Systematic mutagenesis was performed to either make transpose or transition base pair mutants or introduce orthogonal base pairs. Both natural and unnatural base pair mutants were found to improve the biosensor response time without compromising fold turn-on or ligand affinity. These strategies can be transferred to improve the performance of other RNA-based tools.

The discovery of non-canonical bases (NCBs) and development of synthetic xeno-nucleic acids (XNAs) has spawned interest in many applications in viral genomics, synthetic biology and DNA storage. However, inability to do high-throughput sequencing of NCBs has been a significant limitation. We demonstrate that XNAs with NCBs can be robustly sequenced on a MinION system ( > 2.3×10⁶ reads/flowcell) to obtain significantly distinct signals from controls (median fold-change >6×). To enable AI-model training, we synthesized and sequenced a complex pool of 1,024 NCB-containing oligonucleotides with varied 6-mer contexts and high purity ( > 90%). Bootstrapped models assisted in data preparation, and data augmentation with spliced reads provided high context diversity, enabling learning of generalizable models to decipher NCB-containing sequences with high accuracy ( > 80%) and specificity (99%). These results highlight the versatility of nanopore sequencing for interrogating unusual nucleic acids, and the potential to transform the study of genetic material beyond those that use canonical bases.

Bacteriophage T7 RNA polymerase (T7 RNAP) is widely used for synthesizing RNA molecules with synthetic modifications and unnatural base pairs (UBPs) for a variety of biotechnical and therapeutic applications. However, the molecular basis of transcription recognition of UBPs by T7 RNAP remains poorly understood. Here we focused on a representative UBP, 7-(2-thienyl)-imidazo[4,5-b]pyridine (Ds) and pyrrole 2-carbaldehyde (Pa), and investigated how the hydrophobic Ds–Pa pair is recognized by T7 RNAP. Our kinetic assays revealed that T7 RNAP selectively recognizes the Ds or Pa base in the templates and preferentially incorporates their cognate unnatural base nucleotide substrate (PaTP or DsTP) over natural NTPs. Our structural studies reveal that T7 RNAP recognizes the unnatural substrates at the pre-insertion state in a distinct manner compared to natural substrates. These results provide mechanistic insights into transcription recognition of UBP by T7 RNAP and provide valuable information for designing the next generation of UBPs.