Summary
Intracellular organelles that lack a membrane boundary are often formed through liquid-liquid phase separation. The biophysical properties of such structures are linked to their physiological functions and involvement in diseases. Most of these organelles contain RNA molecules that associate with RNA binding proteins (RBPs) to control intracellular phase separation (1). Specific long noncoding RNAs (lncRNAs) are especially important in the architecture of membraneless organelles (2). On page 547 of this issue, Wu et al. (3) provide a mechanistic understanding of how lncRNAs modulate the biophysical properties of phase-separated nucleolar subdomains of the nucleus, where ribosome biogenesis takes place.