Molecular mechanism of pH-dependent modulation of Sup35 phase separation by intrinsically disordered M domain.

Abstract

In budding yeast, starvation stress can trigger a protective response where most cellular processes are downregulated. The transition to this fully reversible state is accompanied by cytoplasmic acidification and subsequent reorganization. Sup35, a translation termination factor with two intrinsically disordered regions (N and M domains), is known to phase separate upon cytoplasmic acidification. Previous work showed the pH dependence of Sup35's phase separation could be attributed to a particularly dense ionizable cluster of negatively-charged residues in the intrinsically disordered M domain, which is proposed to regulate the phase separation properties of the N domain. In this work, we use NMR spectroscopy to probe the pH sensitivity of the ionizable residues in the IDR regions and their interactions. Our aim is to determine the molecular mechanism by which the M domain regulates Sup35's phase separation.