Chemical probing of RNA in living cells

In vivo architecture of the telomerase RNA catalytic core in Trypanosoma brucei

Telomerase is a unique ribonucleoprotein (RNP) reverse transcriptase that utilizes its cognate RNA molecule as a template for telomere DNA repeat synthesis. Telomerase contains the reverse transcriptase protein, TERT and the template RNA, TR, as its core components. The 5'-half of TR forms a highly conserved catalytic core comprising of the template region and adjacent domains necessary for telomere synthesis. However, how telomerase RNA folding takes place in vivo has not been fully understood due to low abundance of the native RNP. Here, using unicellular pathogen Trypanosoma brucei as a model, we reveal important regional folding information of the native telomerase RNA core domains, i.e. TR template, template boundary element, template proximal helix and Helix IV (eCR4-CR5) domain. For this purpose, we uniquely combined in-cell probing with targeted high-throughput RNA sequencing and mutational mapping under three conditions: in vivo (in WT and TERT-/- cells), in an immunopurified catalytically active telomerase RNP complex and ex vivo (deproteinized). We discover that TR forms at least two different conformers with distinct folding topologies in the insect and mammalian developmental stages of T. brucei. Also, TERT does not significantly affect the RNA folding in vivo, suggesting that the telomerase RNA in T. brucei exists in a conformationally preorganized stable structure. Our observed differences in RNA (TR) folding at two distinct developmental stages of T. brucei suggest that important conformational changes are a key component of T. brucei development.

In Vivo and In Vitro Genome-Wide Profiling of RNA Secondary Structures Reveals Key Regulatory Features in Plasmodium falciparum

It is widely accepted that the structure of RNA plays important roles in a number of biological processes, such as polyadenylation, splicing, and catalytic functions. Dynamic changes in RNA structure are able to regulate the gene expression programme and can be used as a highly specific and subtle mechanism for governing cellular processes. However, the nature of most RNA secondary structures in Plasmodium falciparum has not been determined. To investigate the genome-wide RNA secondary structural features at single-nucleotide resolution in P. falciparum, we applied a novel high-throughput method utilizing the chemical modification of RNA structures to characterize these structures. Structural data from parasites are in close agreement with the known 18S ribosomal RNA secondary structures of P. falciparum and can help to predict the in vivo RNA secondary structure of a total of 3,396 transcripts in the ring-stage and trophozoite-stage developmental cycles. By parallel analysis of RNA structures in vivo and in vitro during the Plasmodium parasite ring-stage and trophozoite-stage intraerythrocytic developmental cycles, we identified some key regulatory features. Recent studies have established that the RNA structure is a ubiquitous and fundamental regulator of gene expression. Our study indicate that there is a critical connection between RNA secondary structure and mRNA abundance during the complex biological programme of P. falciparum. This work presents a useful framework and important results, which may facilitate further research investigating the interactions between RNA secondary structure and the complex biological programme in P. falciparum. The RNA secondary structure characterized in this study has potential applications and important implications regarding the identification of RNA structural elements, which are important for parasite infection and elucidating host-parasite interactions and parasites in the environment.

Inforna 2.0: A Platform for the Sequence-Based Design of Small Molecules Targeting Structured RNAs

The development of small molecules that target RNA is challenging yet, if successful, could advance the development of chemical probes to study RNA function or precision therapeutics to treat RNA-mediated disease. Previously, we described Inforna, an approach that can mine motifs (secondary structures) within target RNAs, which is deduced from the RNA sequence, and compare them to a database of known RNA motif-small molecule binding partners. Output generated by Inforna includes the motif found in both the database and the desired RNA target, lead small molecules for that target, and other related meta-data. Lead small molecules can then be tested for binding and affecting cellular (dys)function. Herein, we describe Inforna 2.0, which incorporates all known RNA motif-small molecule binding partners reported in the scientific literature, a chemical similarity searching feature, and an improved user interface and is freely available via an online web server. By incorporation of interactions identified by other laboratories, the database has been doubled, containing 1936 RNA motif-small molecule interactions, including 244 unique small molecules and 1331 motifs. Interestingly, chemotype analysis of the compounds that bind RNA in the database reveals features in small molecule chemotypes that are privileged for binding. Further, this updated database expanded the number of cellular RNAs to which lead compounds can be identified.

Human telomerase reverse transcriptase binds to a pre-organized hTR in vivo exposing its template

Telomerase is a specialized reverse transcriptase that is responsible for telomere length maintenance. As in other organisms, the minimal components required for an active human telomerase are the template-providing telomerase RNA (hTR) and the enzymatic entity telomerase reverse transcriptase (hTERT). Here, we explored the structure of hTR and the hTERT-induced conformational changes within hTR in living cells. By employing an in vivo DMS chemical probing technique, we showed that the pseudoknot and associated triple helical scaffold form stably in vivo independently of hTERT. In fact, the dimethyl-sulfate (DMS) modification pattern suggests that hTR alone is capable of adopting a conformation that is suited to interact with hTERT. However, in the absence of hTERT the template region of hTR is only weakly accessible to DMS-modifications. The predominant change after binding of hTERT to hTR is the exposure of the template region.

The reverse transcription signature of N-1-methyladenosine in RNA-Seq is sequence dependent

The combination of Reverse Transcription (RT) and high-throughput sequencing has emerged as a powerful combination to detect modified nucleotides in RNA via analysis of either abortive RT-products or of the incorporation of mismatched dNTPs into cDNA. Here we simultaneously analyze both parameters in detail with respect to the occurrence of N-1-methyladenosine (m¹A) in the template RNA. This naturally occurring modification is associated with structural effects, but it is also known as a mediator of antibiotic resistance in ribosomal RNA. In structural probing experiments with dimethylsulfate, m¹A is routinely detected by RT-arrest. A specifically developed RNA-Seq protocol was tailored to the simultaneous analysis of RT-arrest and misincorporation patterns. By application to a variety of native and synthetic RNA preparations, we found a characteristic signature of m¹A, which, in addition to an arrest rate, features misincorporation as a significant component. Detailed analysis suggests that the signature depends on RNA structure and on the nature of the nucleotide 3′ of m¹A in the template RNA, meaning it is sequence dependent. The RT-signature of m¹A was used for inspection and confirmation of suspected modification sites and resulted in the identification of hitherto unknown m¹A residues in trypanosomal tRNA.