When cells encounter heat, they undergo a number of archetypal intracellular changes: global
attenuation of translation, synthesis of molecular chaperones, and the formation of intracellular protein
aggregates. These aggregates were long thought to be the result of misfolded proteins, however, recent work
has suggested that these assemblies may be the adaptive result of biomolecular condensation. It has
remained unclear how biomolecular condensation functions to help cells survive heat stress. Here, I propose to
investigate a connection between heat-induced condensation and translation of molecular chaperones.
Previous work has demonstrated that poly(A)-binding protein (Pab1) condenses during heat shock in
yeast and disrupting Pab1 condensation impairs cellular growth during stress, indicating that stress-triggered
condensation of Pab1 is a part of the adaptive stress response. This finding motivated me to investigate why
Pab1 is important for cell growth during stress. Pab1 acts as a translational repressor by binding transcripts
with A-rich 5’ Untranslated Regions (5’UTRs), including its own transcript. Interestingly, the transcripts of
molecular chaperones produced during stress have A-rich 5’UTRs, and these molecular chaperones go on to
re-solubilize Pab1. My preliminary work shows that soluble Pab1 can repress translation of endogenous
transcripts with A-rich 5’UTRs, while Pab1 condensation inhibits this effect. This suggests an autoregulatory
mechanism through which heat-triggered condensation of Pab1 facilitates high level translation of stress-
induced chaperones, whose capacity to re-solubilize Pab1 leads to repressed translation after sufficient
chaperones have been produced.
To test this model, I will probe the molecular basis of Pab1 translational repression using in vitro
translation assays and fluorescence anisotropy. I will also carry out a bioinformatic analysis of A-rich 5’UTRs to
identify sequence features that are conserved and test whether they contribute to Pab1 repression. Next, I will
design yeast strains to perturb Pab1 condensation in vivo to test how this change affects the production of
molecular chaperones. Finally, Pab1 condensation does not completely explain how heat shock transcripts are
specifically translated in the midst of global translational attenuation, so I will investigate how A-rich 5’UTRs
can promote selective translation, using similar in vitro and in vivo methods. My proposed model connects
direct environmental sensing by condensation to the adaptive cellular stress response and helps shape our
understanding of how cells respond to heat in other contexts, such as immune cells in fever.
This research will be done at the University of Chicago with Dr. D. Allan Drummond and will build my
skillset in in vitro, in vivo, and computational biology, preparing me for a career as an independent investigator.