cerevisiae is dependent on the primary structure of the Sup35 prion domain

Molecular memory of [PSr] prion strains in S.

cerevisiae is dependent on the primary structure of the Sup35 prion domain

Colin G. Crist, Tom Nakayashiki, Hiroshi Kurahashi and Yoshikazu Na- kamura

Department of Basic Medical Sciences, Institute of Medical Science, Uni- versity of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639 Japan

<e-mail> cgcrist@ims.u-tokyo.ac.jp

Abstract

How prions generate and propagate variation in both mammals and yeast is a topic of great interest and increasing evidence indicates that the tertiary or quaternary structure of prion conformations determines the strain phe- notype. Whether or not the conformational information of specific prion 'strains' is transmissible to heterologous prion domains at the molecular level and whether this corresponds to a phenotypic change at the 'strain' level was investigated using the [PSr] prion model of S. cerevisiae.

The prion domain (PrD) of the yeast translation termination factor Sup35 governs a heritable conformational change, analogous to PrP^'', leading to a nonsense suppressor phenotype termed [PSI^]. Since the oli- gopeptide repeat region of the PrD is known to influence [PSr] stability and conformational conversion efficiency, targeted mutations were con- structed within this region to probe its role in stably propagating [PSr]

strains. These variant Sup35s replaced wild-type Sup35 in existing weak and strong [PSr] strains and were investigated for their influence on sta- bility, conformational conversion frequency, and nonsense suppression ef- ficiency.

Variant Sup35s containing a glycine to tyrosine change flanking the 3' end of the oligopeptide repeats increased nonsense suppression efficiency and stability of [PSI^] strains by increasing the efficiency of conforma- tional conversion to [PSr]. Nevertheless, the structural information gov- erning the original [PSr] strains was templated to the variant Sup35s ac-

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curately and therefore the original [PSr] strains were remembered upon return to wild-type Sup35.

Prions have the remarkable capacity to generate phenotypic diversity

and propagate this diversity faithfully. These results indicate that the

primary structure of the PrD is a major determinant of faithful propagation

of prion strains. A mechanism of 'molecular memory' to remember

original [PSI^] strains during transmission amongst heterologous PrDs is

proposed.