Intrinsically disordered regions of tristetraprolin and DCP2 directly interact to mediate decay of ARE-mRNA.

The RNA-binding protein tristetraprolin (TTP) is a potent activator of mRNA decay, specifically for transcripts bearing AU-rich elements (AREs) in their 3'-untranslated regions. TTP functions as a mediator for mRNA decay by interacting with the decay machinery and recruiting it to the target ARE-mRNA. In this study, we report a weak, but direct interaction between TTP and the human decapping enzyme DCP2, which impacts the stability of ARE transcripts. The TTP-DCP2 interaction is unusual as it involves intrinsically disordered regions (IDRs) of both binding partners. We show that the IDR of DCP2 has a propensity for oligomerization and liquid-liquid phase separation in vitro. Binding of TTP to DCP2 leads to its partitioning into phase-separated droplets formed by DCP2, suggesting that molecular crowding might facilitate the weak interaction between the two proteins and enable assembly of a decapping-competent mRNA-protein complex on TTP-bound transcripts in cells. Our studies underline the role of weak interactions in the cellular interaction network and their contribution towards cellular functionality.