Prions of fungi: inherited structures and biological roles

Abstract

There are six fungal prions: four are self-propagating amyloids and two are self-activating enzymes. [URE3] is a prion of the nitrogen catabolism regulator Ure2p; [PSI⁺] is a prion of the translation-termination factor Sup35p; [PIN⁺] is a prion of Rnq1p (function unknown); [Het-s] is a prion of the heterokaryon incompatibility protein HETs; [β] is a prion of vacuolar protease B; and [C] is a prion of a mitogen-activated protein kinase kinase kinase. The infectious amyloid of Sup35p has a parallel in-register β-sheet structure. The [Het-s] prion of Podospora anserina apparently benefits its host, but the [URE3] and [PSI⁺] prions of Saccharomyces cerevisiae are detrimental. Chaperones catalyse amyloid filament breakage to form new seeds, and probably have other roles in prion propagation and generation as well. Different prion variants, with the same protein sequence, have different amyloid structures. Variants can determine host range and chaperone effects.