NEW CHEMICAL TOOLS TO INVESTIGATE RNA FUNCTIONS
Dayie, Theodore K
Sintim, Herman O
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Ribonucleic acid (RNA), as one of the essential macromolecules of life, plays an active role in gene regulation, catalysis, and signaling because of its ability to adopt complex 3D structures that can exist in multiple conformations. Until now, RNA preparation methods devised by most investigators utilized partially denatured the RNA. The mis-folding caused by denaturing - renaturing can seriously affect RNA structure and functional activity. To test this hypothesis, in PART I of this dissertation, we presented a simple strategy using `click' chemistry to couple biotin to a `caged' photocleavable guanosine monophosphate to synthesize native RNAs that are properly folded. We demonstrated that RNA ribozymes, ranging in size from 27 to 527 nt, prepared by our non-denaturing method form a homogenous population with superior catalytic activity than those prepared by traditional refolding methods. Having developed a method for in vitro RNA synthesis, we studied the riboswitch family of RNAs that require remolding their structure for function in PART II. C-di-GMP riboswitch, as the only currently known secondary messenger riboswitch, senses c-di-GMP using its aptamer domain to modulate the expression of genes which affects biofilm formation and virulence factors production in bacteria. To specifically target pathogenic bacteria in polymicrobial systems that control the RNA-mediated c-di-GMP signaling pathway through riboswitch regulation, different c-di-GMP analogs have been used as chemical tools to investigate the structure-activity relationship (SAR) of c-di-GMP binding to different c-di-GMP riboswitches. We demonstrated that different 2'-position modified c-di-GMP analogs could differentiate between two different classes of c-di-GMP riboswitches and even bind to one particular riboswitch in class I with different affinities. Specifically, Clostridium tetani (Ct-E88) RNA in class I c-di-GMP riboswitch was used for (structural dynamic) study to understand how ligand binding drives the conformational change to regulate the downstream genes within the expression platform. Our preliminary data obtained via different biochemical and biophysical tools - such as selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE), small-angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) spectroscopy - demonstrated that Mg2+ ions accelerate ligand recognition by pre-organizing the RNA, and then rapid ligand binding folds the RNA into a compact structure for likely downstream gene regulation.