Ssb1 chaperone is a [PSI+] prion-curing factor

Yeast SUP7 or SUP11 nonsense suppressors have no phenotypic expression in s trains deficient in the isopentenylation of A37 in tRNA. Here we show that such strains spontaneously produce cells with a nonsense suppressor phenoty pe which is related to the cytoplasmically inherited determinant and manife sts all the key features of the [PSI+] prion. A screen of a multicopy yeast genomic library for genes that inactivate the [PSI+]-related suppressor ph enotype resulted in the isolation of the SSB1 gene. Moreover, we demonstrat e that multicopy plasmid encoding the Ssb1 chaperone cures cells of the [PS I+] prion.