Abstract 2419 Evolutionary rewiring of the dynamic network within the NS1 protein of influenza A virus

Molecular chaperones play a pivotal role in maintaining proteostasis under normal conditions by regulating the heat shock response (HSR), refolding misfolded proteins, and disassembling aggregates.Under transient stress, such as heat shock, certain proteins and RNAs assemble into membrane-less, protective organelles called stress granules (SGs), while a heat shock response (HSR) is activated to upregulate the expression of chaperones.Once stress subsides, the upregulated chaperone network efficiently disassembles SGs.Hsp70s, specifically the constitutive isoforms Ssa1 and Ssa2, are central players in this disassembly process and eventually are responsible for HSR repression.While Hsp70s have a role after heat shock, it is unclear whether Hsp70s play a role in limiting non-canonical aggregation in normal conditions when HSR is low.Using a yeast ssa1Dssa2D double knockout which has an elevated HSR, we found that the stress responsive Poly-A binding protein, Pab1, unexpectedly forms large cytoplasmic inclusions when fused to GFP.Introduction of the chaperones, Ssa1, Sis1, or Hsp104 limited Pab1 inclusion formation under normal conditions, suggesting that any one of these chaperones can override the aberrant Pab1 aggregation in ssa1Dssa2D cells.Under stress conditions, the mutant cells formed both canonical small stress granules and large inclusions.While it is not surprising that stress granules disassembled in ssa1Dssa2D cells, the large inclusions also disassembled, albeit at a slower rate.We suspect that the loss of the large inclusion over time is due to increased chaperone levels caused by the elevated HSR.