Dedon, P. C. | bioRxiv Science

bioRxiv2019

Quantifying the RNA cap epitranscriptome reveals novel caps in cellular and viral RNA

Chemical modification of transcripts with 5 caps occurs in all organisms. Here we report a systems-level mass spectrometry-based technique, CapQuant, for quantitative analysis of the cap epitranscriptome in any organism. The method was piloted with 21 canonical caps - m7GpppN, m7GpppNm, GpppN, GpppNm, and m2,2,7GpppG - and 5 \"metabolite\" caps - NAD, FAD, UDP-Glc, UDP-GlcNAc, and dpCoA. Applying CapQuant to RNA from purified dengue virus, Escherichia coli, yeast, mice, and humans, we discovered four new cap structures in humans and mice (FAD, UDP-Glc, UDP-GlcNAc, and m7Gpppm6A), cell- and tissue-specific variations in cap methylation, and surprisingly high proportions of caps lacking 2-O-methylation, such as m7Gpppm6A in mammals and m7GpppA in dengue virus, and we did not detect cap m1A/m1Am in humans. CapQuant accurately captured the preference for purine nucleotides at eukaryotic transcription start sites and the correlation between metabolite levels and metabolite caps. The mystery around cap m1A/m1Am analysis remains unresolved.

systems biology↗

bioRxiv2019

Transcriptome-wide dynamics of extensive m6A mRNA methylation during Plasmodium falciparum blood-stage development

Malaria pathogenesis results from the asexual replication of Plasmodium falciparum within human red blood cells, which relies on a precisely timed cascade of gene expression over a 48-hour life cycle. Although substantial post-transcriptional regulation of this hardwired program has been observed, it remains unclear how these processes are mediated on a transcriptome-wide level. To this end, we identified mRNA modifications in the P. falciparum transcriptome and performed a comprehensive characterization of N6-methyladenosine (m6A) over the course of blood stage development. Using mass spectrometry and m6A RNA sequencing, we demonstrate that m6A is highly developmentally regulated, exceeding m6A levels known in any other eukaryote. We identify an evolutionarily conserved m6A writer complex and show that knockdown of the putative m6A methyltransferase by CRISPR interference leads to increased levels of transcripts that normally contain m6A. In accordance, we find an inverse correlation between m6A status and mRNA stability or translational efficiency. Our data reveal the crucial role of extensive m6A mRNA methylation in dynamically fine-tuning the transcriptional program of a unicellular eukaryote as well as a new epitranscriptomic layer of gene regulation in malaria parasites.

molecular biology↗