INVESTIGATE SEQUENCE SPECIFICITY IN THE BIOSYNTHESIS AND RECOGNITION OF RNA CHEMICAL MODIFICATIONS - INVESTIGATE SEQUENCE SPECIFICITY IN THE BIOSYNTHESIS AND RECOGNITION OF RNA CHEMICAL MODIFICATIONS PROJECT SUMMARY Chemical modifications are prevalent in the cellular RNA across all domains of life; they expand the chemical space beyond the four natural building blocks of RNA, modulate folding, intermolecular interactions involving RNA, and regulate gene expression. Growing evidence shows that several RNA chemical modifications can be reversed by endogenous enzymes and can respond to external cues, including metabolic signaling, nutrient starvation, oxidative stress, and temperature change. Interestingly, many proteins known to directly or indirectly regulate RNA chemical modifications are found to be dysregulated in physiological defects or diseases, forming the basis of many exciting hypotheses to discover the role of the epitranscriptome in gene expression regulation. While our understanding and therapeutic exploitation of epitranscriptome-based gene expression control continue to expand, the molecular mechanisms that govern this regulation remain poorly understood. A critical question in the epitranscriptome field is the sequence specificity of various RNA modifications: how they are installed on specific sequence locations and how they regulate specific protein-RNA recognition. Studying the sequence contexts of chemically modified endogenous RNA has been technically challenging. With recent advances in high-throughput sequencing-based technologies, we can now map and quantify only a handful of RNA chemical modifications (out of over 150 types) in their native sequence contexts inside cells. The pilot mapping studies revealed conserved sequence elements associated with the occurrence of specific modifications across different domains of life. That such conserved occurrence of modifications, rather than being randomly distributed, strongly suggests the involvement of dedicated endogenous machinery that regulates modifications with high specificity. However, we do not understand why and how the modifications are installed at specific locations and regulate biology, most likely in a sequence-dependent manner. To address this knowledge gap, we need methods to detect RNA modifications confidently within sequence contexts that offer high accuracy and throughput. Here we propose a program focusing on developing such methods and performing systematic biochemical characterization of the sequence specificity of effector proteins by combining in vitro high-throughput assay and in cellulo massive parallel reporter assay approaches. Inspired by recent findings that modification reader proteins may recognize more than one chemical modification, we aim to revisit the molecular recognition mechanism of the most heavily modified RNA – transfer RNAs in human cells. By developing more advanced detection tools in mapping RNA chemical modifications in biological RNA and designed oligonucleotide libraries modified in vitro or in cellular reporter assays, we will elucidate the fundamental biochemical properties of the critical regulators of the epitranscriptome with unprecedented efficiency and comprehensiveness, leading to a better understanding of RNA regulation, and new opportunities to exploit and control the epitranscriptome.
