Targeted RNA Condensation in Living Cells via Genetically Encodable Triplet Repeat Tags.

Living systems contain various functional membraneless organelles that can segregate selective proteins and RNAs via liquid-liquid phase separation. Inspired by nature, many synthetic compartments have been engineered in vitro and in living cells, mostly focused on protein-scaffolded systems. Herein, we introduce a nature-inspired genetically encoded RNA tag to program cellular condensate formations and recruit non-phase-transition target RNAs to achieve functional modulation. In our system, different lengths of CAG-repeat tags were tested as the self-assembled scaffold to drive multivalent condensate formation. Various selective target messenger RNAs and noncoding RNAs can be compartmentalized into these condensates. With the help of fluorogenic RNA aptamers, we have systematically studied the formation dynamics, spatial distributions, sizes, and densities of these cellular RNA condensates. The regulation functions of these CAG-repeat tags on the cellular RNA localization, lifetime, RNA-protein interactions, and gene expression have also been investigated. Considering the importance of RNA condensation in both health and disease conditions, these genetically encodable modular and self-assembled tags can be potentially widely used for chemical biology and synthetic biology studies.