The TIS granule is a filamentous condensate that shares a large surface area with the rough endoplasmic reticulum and is involved in membrane protein trafficking. Large unstructured areas in mRNAs which exist in Tis granule have a high proclivity for forming a ubiquitous intermolecular interaction network, which act as the condensate skeleton. Because the underlying RNA network precludes full fusing of spherical liquid-like condensates, Tis granule is an irregularly shaped membrane-less organelles. The large surface area created by the condensate surface and the interface with other organelles could enhance interactions. (33650968).
Formation, Composition & dynamics (Assembly and disassembly)
Multiple AU-rich regions are enriched in membrane protein-encoding mRNAs by the TIs granule. TIS granules are interwoven with the endoplasmic reticulum to produce a reticular meshwork (ER). TIS granules and the ER form a subcellular compartment called the TIGER domain, which is biophysically and biochemically separate from the cytoplasm. This compartment facilitates SET's interaction with membrane proteins via the 3'UTR, allowing for enhanced surface expression and functional variety of proteins like as CD47 and PD-L1. The TIGER domain is a subcellular compartment that allows for the creation of specialized and functionally relevant protein-protein interactions that are not possible to establish outside of the cell (30449617).
Ma W, Zheng G, Xie W, Mayr C. In vivo reconstitution finds multivalent RNA-RNA interactions as drivers of mesh-like condensates. Elife. 2021 Mar 2;10:e64252. doi: 10.7554/eLife.64252. PMID: 33650968; PMCID: PMC7968931.
Ma W, Mayr C. A Membraneless Organelle Associated with the Endoplasmic Reticulum Enables 3'UTR-Mediated Protein-Protein Interactions. Cell. 2018 Nov 29;175(6):1492-1506.e19. doi: 10.1016/j.cell.2018.10.007. Epub 2018 Nov 15. PMID: 30449617; PMCID: PMC6711188.