Question

In order for yeast to be in the [PSI⁺] state, they need to express a chaperone called HSP104. If HSP104 is deleted, [PSI⁺] reverts to [PSI^-] over time. HSP104 is a disaggregase that “breaks” (or “fragments”) large protein aggregates into smaller aggregates. Explain why HSP104 is needed to maintain the [PSI⁺] state in yeast.

Answer 1

The [PSI+] yeast prion forms due the misfolding of Sup35 protein to form amyloid aggregates. The prion is dependent on the molecular chaperone protein namesd Hsp104. Hsp104, as mentioned, is a disaggregase that breaks large protein aggregated into smaller ones. The prions for seeds, which are essentially large aggregates. The Hsp104 chaperone severes these seeds and help them pass on when a yeast cell divides. In absence of the chaperone, the seeds are not broken, and they eventually dilute out with increasing rounds of cell division. Thus , Hsp104 is needed to maintain the [PSI+] in yeast.