Genetic study of interactions between the cytoskeletal assembly protein Sla1 and prion-forming domain of the release factor Sup35 (eRF3) in Saccharomyces cerevisiae

Striking similarities between cytoskeletal assembly and the "nucleated poly merization" model of prion propagation suggest that similar or overlapping sets of proteins may assist in both processes. We show that the C-terminal domain of the yeast cytoskeletal assembly protein Sla1 (Sla1C) specifically interacts with the N-terminal prion-forming domain (Sup35N) of the yeast r elease factor Sup35 (eRF3) in the two-hybrid system. Sla1C and several othe r Sup35N-interacting proteins also exhibit two-hybrid interactions with the poly-Gin-expanded N-proximal fragment of human huntingtin, which promotes Huntington disease-associated aggregation. The Sup35N-Sla1C interaction is inhibited by Sup35N alterations that make Sup35 unable to propagate the [PS I+] state and by the absence of the chaperone protein Hsp104, which is esse ntial for [PSI] propagation. In a Sla1(-) background, [PSI] curing by dimet hysulfoxide or excess Hsp104 is increased, while translational readthrough and de novo [PSI] formation induced by excess Sup35 or Sup35N are decreased . These data show that, in agreement with the proposed function of Sla1 dur ing cytoskeletal formation, Sla1 assists in [PSI] formation and propagation , but is not required for these processes. Sla1(-) strains are sensitive to some translational inhibitors, and some sup35 mutants, obtained in a Sla1( -) background, are sensitive to Sla1, suggesting that the interaction betwe en Slal and Sup35 proteins may play a role in the normal function of the tr anslational apparatus. We hypothesize that Sup35N is involved in regulatory interactions with intracellular structural networks, and [PSI] prion may b e formed as a by-product of this process.