IN-VITRO PROPAGATION OF THE PRION-LIKE STATE OF YEAST SUP35 PROTEIN

The yeast cytoplasmically inherited genetic determinant [PSI+] is pres umed to be a manifestation of the prion-like properties of the Sup35 p rotein (Sup35p). Here, cell-free conversion of Sup35p from [psi(-)] ce lls (Sup35(psi-)) to the prion-like [PSI+]-specific form (Sup35p(PSI+) ) was observed. The conversion reaction could be repeated for several consecutive cycles, thus modeling in vitro continuous [PSI+] propagati on. Size fractionation of lysates of [PSI+] cells demonstrated that th e converting activity was associated solely with Sup35p(PSI+) aggregat es, which agrees with the nucleation model for [PSI+] propagation. Sup 35p(PSI+) was purified and showed high conversion activity, thus confi rming the prion hypothesis for Sup35p.