Polyurethanes (PUs) have many applications resulting from their preeminent properties, but being commonly used toxic catalysts, and the lack of processability for PU thermosets cause limitations. Herein, we report a new class of the PU-like dynamic covalent polymers, poly(oxime-urethanes) (POUs), which are prepared from the uncatalyzed polyaddition of multifunctional oximes and hexamethylene diisocyanate (HDI) at ambient temperature. Kinetics studies reveal that almost complete polymerization (∼99% conversion) can be achieved in 3 h at 30 °C in dichloromethane (DCM), the most effective among the solvents evaluated, producing linear POUs with comparable molecular weights to the catalyzed PUs. We find that the oxime-carbamate structures are reversible at about 100 °C through oxime-enabled transcarbamoylation via a thermally dissociative mechanism. The cross-linked POUs based on oxime-carbamate bonds show efficient catalyst-free healable/recyclable properties. Density functional theory (DFT) calculations suggest that the fast oxime-urethanation and the mild thermoreversible nature are mediated by the characteristic nitrone tautomer of the oxime. Given widespread urethane-containing materials, POUs are of promising potential in applications because of the excellent mechanical performances, facile preparation, and dynamic property without using catalysts.

Argonaute-associated siRNAs and Piwi-associated piRNAs have overlapping roles in silencing mobile genetic elements in animals. In Caenorhabditis elegans, mutator (mut) class genes mediate siRNA-guided repression of transposons as well as exogenous RNAi, but their roles in endogenous RNA silencing pathways are not well-understood. To characterize the endogenous small RNAs dependent on mut class genes, small RNA populations from a null allele of mut-16 as well as a regulatory mut-16(mg461) allele that disables only somatic RNAi were subjected to deep sequencing. Additionally, each of the mut class genes was tested for a requirement in 26G siRNA pathways. The results indicate that mut-16 is an essential factor in multiple endogenous germline and somatic siRNA pathways involving several distinct Argonautes and RNAdependent RNA polymerases. The results also reveal essential roles for mut-2 and mut-7 in the ERGO-1 class 26G siRNA pathway and less critical roles for mut-8, mut-14, and mut-15. We show that transposons are hypersusceptible to mut-16-dependent silencing and identify a requirement for the siRNA machinery in piRNA biogenesis from Tc1 transposons. We also show that the somaspecific mut-16(mg461) mutant allele is present in multiple C. elegans laboratory strains. RNAi can be elicited by the introduction of dsRNAs, which trigger sequence-specific degradation of homologous mRNAs (1). Exogenous dsRNAs are processed into ∼22-nt siRNA duplexes by the RNase III enzyme DICER (2-4). One strand of the siRNA duplex is loaded into a silencing complex (RISC) containing an Argonaute protein and accessory factors, where it serves as a guide to silence complementary mRNAs (reviewed in ref. 5).High-throughput sequencing has revealed an extensive repertoire of endogenous siRNAs in plants, animals, and fungi. These endogenous siRNAs play roles in maintaining genome integrity at both transcriptional and posttranscriptional levels by suppressing transposon mobilization, silencing aberrant transcripts, regulating gene expression, and promoting heterochromatin formation (reviewed in ref. 6). In the nematode Caenorhabditis elegans, endogenous siRNAs can be broadly categorized according to their length and 5′ nucleotide. 22G siRNAs are predominantly 22 nt in length and contain a 5′G that is triphosphorylated, whereas 26G siRNAs are predominantly 26 nt long and have a 5′G that is monophosphorylated. These distinct siRNA classes are bound to particular subtypes of the 27 different C. elegans Argonaute proteins (WAGOs, CSR-1, ALG-3/4, and ERGO-1), which are largely responsible for conferring unique functionality to the different classes of siRNAs. The majority of endogenous siRNAs in C. elegans bypass DICER processing and instead, derive from short RNA-dependent RNA polymerase (RdRP) transcripts, which likely undergo additional nuclease-mediated processing to facilitate association with one particular type of Argonaute protein (7-9). C. elegans contains four RdRPs (ego-1, rrf-1, rrf-2, and rrf-3) with overlapping roles in the various s...

More than 100 modifications have been found in RNA. Analogous to epigenetic DNA methylation, epitranscriptomic modifications can be written, read, and erased by a complex network of proteins. Apart from N6-methyladenosine (m6A), N1-methyladenosine (m1A) has been found as a reversible modification in tRNA and mRNA. m1A occurs at positions 9, 14, and 58 of tRNA, with m1A58 being critical for tRNA stability. Other than the hundreds of m1A sites in mRNA and long non-coding RNA transcripts, transcriptome-wide mapping of m1A also identifies >20 m1A sites in mitochondrial genes. m1A in the coding region of mitochondrial transcripts can inhibit the translation of the corresponding proteins. In this review, we summarize the current understanding of m1A in mRNA and tRNA, covering high-throughput sequencing methods developed for m1A methylome, m1A-related enzymes (writers and erasers), as well as its functions in mRNA and tRNA.