Site-Specific DNA Functionalization through the Tetrazene-Forming Reaction in Ionic Liquids

Development of multiple chemical tools for deoxynucleic acid (DNA) labeling has facilitated wide use of their functionalized conjugates, but significant practical and methodological challenges remain to achievement of site-specific chemical modification of the biomacromolecule. As covalent labeling processes are more challenging in aqueous solution, use of nonaqueous, biomolecule-compatible solvents such as an ionic liquid consisting of a salt with organic molecule architecture, could be remarkably helpful in this connection. Herein, we demonstrate site-specific chemical modification of DNAs through a tetrazene-forming amine-azide coupling reaction using an ionic liquid. This ionic liquid-enhanced reaction process has good functional group tolerance and precise chemoselectivity, and enables incorporation into DNA of various useful functionalities such as biotin, cholesterol and fluorophores which could be incorporated into DNA through this method. A site-specifically labeled single stranded nucleotide, or aptamer interacting with a growth factor receptor (Her2) was successfully used in the fluorescence imaging of breast cancer cell lines. The non-traditional medium-promoted labeling strategy described here provides an alternative design paradigm for future development of chemical tools for applications involving DNA functionalization.

Photocontrol of CRISPR/Cas9 function by site-specific chemical modification of guide RNA

The CRISPR/Cas9 function is optically controlled in living cells by the site-specifically caged guide RNA based on the RNA–protein interaction.

Use of a Yeast TRNase Killer Toxin to Diagnose Kti12 Motifs Required for TRNA Modification by Elongator

Saccharomyces cerevisiae cells are killed by zymocin, a tRNase ribotoxin complex from Kluyveromyces lactis, which cleaves anticodons and inhibits protein synthesis. Zymocin’s action requires specific chemical modification of uridine bases in the anticodon wobble position (U34) by the Elongator complex (Elp1-Elp6). Hence, loss of anticodon modification in mutants lacking Elongator or related KTI (K. lactis Toxin Insensitive) genes protects against tRNA cleavage and confers resistance to the toxin. Here, we show that zymocin can be used as a tool to genetically analyse KTI12, a gene previously shown to code for an Elongator partner protein. From a kti12 mutant pool of zymocin survivors, we identify motifs in Kti12 that are functionally directly coupled to Elongator activity. In addition, shared requirement of U34 modifications for nonsense and missense tRNA suppression (SUP4; SOE1) strongly suggests that Kti12 and Elongator cooperate to assure proper tRNA functioning. We show that the Kti12 motifs are conserved in plant ortholog DRL1/ELO4 from Arabidopsis thaliana and seem to be involved in binding of cofactors (e.g. nucleotides, calmodulin). Elongator interaction defects triggered by mutations in these motifs correlate with phenotypes typical for loss of U34 modification. Thus, tRNA modification by Elongator appears to require physical contact with Kti12, and our preliminary data suggest that metabolic signals may affect proper communication between them.

Prober: A general toolkit for analyzing sequencing-based ‘toeprinting’ assays

SUMMARYA number of high-throughput transcriptase drop-off assays have recently been developed to probe post-transcriptional dynamics of RNA-protein interaction, RNA structure, and post-transcriptional modifications. Although these assays survey a diverse set of ‘epitranscriptomic’ marks, they share methodological similarities and as such their interpretation is predicated on addressing similar computational challenges. Among these, a key question is how to learn isoform-specific chemical modification profiles in the face of complex read multi-mapping. In this paper, we propose PROBer, the first rigorous statistical model to handle these challenges for a general set of sequencing-based ‘toeprinting’ assays.