Amyloid Diversity, Translation, and the Yeast Prion [PSI+]

Yeast prions have proved to be an excellent model for learning about the biophysical properties of prions. In particular, the [PSI+] prion has been invaluable for elucidating the structural basis of prion strains and the prion species barrier. The [PSI+] prion itself is an aggregated form of the translation termination factor Sup35. The aggregation of Sup35 into beta-sheet rich amyloid fibers reduces its activity levels, resulting in translational readthrough of stop codons. In this dissertation, I explore the diversity of amyloid structures formed by a chimeric Sup35 protein, and describe my work to investigate the translational effects of the [PSI+] prion.In the first section, I describe my work examining the amyloid structure of a chimeric yeast prion that is able to form two species-specific conformations. These conformations were probed by hydrogen/deuterium exchange and nuclear magnetic resonance, a technique that has been successfully applied to the study of many amyloids. I discovered that these two conformations were radically different: the residues that comprised the "amyloid core" of each conformation was entirely distinct from the other. In addition to emphasizing the diversity of amyloid formation, this result also reveals that amyloid formation in one region of a polypeptide can preclude the formation of amyloid in another amyloidogenic sequence in the same polypeptide.In the second section, I describe an investigation into the translational effects of the yeast prion [PSI+] by using a technique called ribosome profiling. Ribosome profiling takes advantage of next-generation sequencing technologies to deeply sequence the short fragments that are protected by ribosomes. We can examine the differences in translation in [PSI+] and isogenic [psi-] yeast strains to uncover the regulatory effects of this yeast prion