**Izzy Owen and Frank Shewmaker \***

Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA; izzy.owen@usuhs.edu

**\*** Correspondence: fshewmaker@usuhs.edu; Tel.: +1-301-295-3527

Received: 11 October 2019; Accepted: 2 November 2019; Published: 5 November 2019

**Abstract:** Advances in genomics and proteomics have revealed eukaryotic proteomes to be highly abundant in intrinsically disordered proteins that are susceptible to diverse post-translational modifications. Intrinsically disordered regions are critical to the liquid–liquid phase separation that facilitates specialized cellular functions. Here, we discuss how post-translational modifications of intrinsically disordered protein segments can regulate the molecular condensation of macromolecules into functional phase-separated complexes.

**Keywords:** liquid–liquid phase separation; intrinsically disordered regions; post-translational modifications; membraneless organelles
