The three faces of Sup35.

Abstract

Sup35p is an essential protein in yeast that functions in complex with Sup45p for efficient translation termination. Although some may argue that this function is the only important attribute of Sup35p, there are two additional known facets of Sup35p's biology that may provide equally important functions for yeast; both of which involve various strategies for coping with stress. Recently, the N-terminal and middle regions (NM) of Sup35p, which are not required for translation termination function, have been found to provide stress-sensing abilities and facilitate the phase separation of Sup35p into biomolecular condensates in response to transient stress. Interestingly, the same NM domain is also required for Sup35p to misfold and enter into aggregates associated with the [PSI+ ] prion. Here, we review these three different states or "faces" of Sup35p. For each, we compare the functionality and necessity of different Sup35p domains, including the role these domains play in facilitating interactions with important protein partners, and discuss the potential ramifications that each state affords yeast cells under varying environmental conditions.