[PSI+] prion propagation is controlled by inositol polyphosphates.

Abstract

The yeast prions [PSI+] and [URE3] are folded in-register parallel β-sheet amyloids of Sup35p and Ure2p, respectively. In a screen for antiprion systems curing [PSI+] without protein overproduction, we detected Siw14p as an antiprion element. An array of genetic tests confirmed that many variants of [PSI+] arising in the absence of Siw14p are cured by restoring normal levels of the protein. Siw14p is a pyrophosphatase specifically cleaving the β phosphate from 5-diphosphoinositol pentakisphosphate (5PP-IP₅), suggesting that increased levels of this or some other inositol polyphosphate favors [PSI+] propagation. In support of this notion, we found that nearly all variants of [PSI+] isolated in a WT strain were lost upon loss of <i>ARG82</i>, which encodes inositol polyphosphate multikinase. Inactivation of the Arg82p kinase by D131A and K133A mutations (preserving Arg82p's nonkinase transcription regulation functions) resulted the loss of its ability to support [PSI+] propagation. The loss of [PSI+] in <i>arg82</i>Δ is independent of Hsp104's antiprion activity. [PSI+] variants requiring Arg82p could propagate in <i>ipk1</i>Δ (IP₅ kinase), <i>kcs1</i>Δ (IP₆ 5-kinase), <i>vip1</i>Δ (IP₆ 1-kinase), <i>ddp1</i>Δ (inositol pyrophosphatase), or <i>kcs1</i>Δ <i>vip1</i>Δ mutants but not in <i>ipk1</i>Δ <i>kcs1</i>Δ or <i>ddp1</i>Δ <i>kcs1</i>Δ double mutants. Thus, nearly all [PSI+] prion variants require inositol poly-/pyrophosphates for their propagation, and at least IP₆ or 5PP-IP₄ can support [PSI+] propagation.