Kinetic Analysis of Prion Propagation and Quantitative Analysis of Genetic Interactions in Yeast

Through a series of kinetic and biophysical experiments on a purified recombinant fragment of Sup35p, I have found that assembly can occur by the direct addition of monomer subunits to the ends of growing fibers without any obligatory oligomeric intermediates. As nonfibrillar oligomeric species have been suggested to be the source of toxicity in amyloid diseases, this result indicates that fiber formation may actually be a reaction that is competing with, rather than resulting from, the formation of toxic aggregates. I have also found that new fibers are formed more readily by the fragmentation of existing fibers than by de novo nucleation, and I have proposed a kinetic mechanism for fiber assembly which is consistent with existing data.