EC Accepts, published online ahead of print on 1 May 2009

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Eukaryotic Cell doi:10.1128/EC.00353-08
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Increased [PSI⁺] appearance by fusion of Rnq1 with the prion domain of Sup35 in Saccharomyces cerevisiae

Young-Jun Choe, Yangkyun Ryu, Hyun-Jin Kim, and Yeong-Jae Seok^*

From the Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea

^* To whom correspondence should be addressed. Email: yjseok{at}snu.ac.kr.

During propagation, yeast prions show a strict sequence preference that confers the specificity of prion assembly. Although propagations of [PSI⁺] and [RNQ⁺] are independent of each other, the appearance of [PSI⁺] is facilitated by the presence of [RNQ⁺]. To explain the [RNQ⁺] effect on the [PSI⁺] appearance, the cross-seeding model was suggested in which Rnq1 aggregates act as imperfect templates for Sup35 aggregation. If cross-seeding events take place in the cytoplasm of yeast cells, a collision frequency between Rnq1 aggregates and Sup35 will affect the appearance of [PSI⁺]. In this study, to address whether cross-seeding occurs in vivo, a new [PSI⁺] induction method was developed that exploits a protein fusion between the prion domain of Sup35 (NM) and Rnq1. This fusion protein successfully joined preexisting Rnq1 aggregates, which should result in the localization of NM around the Rnq1 aggregates and hence the increased collision frequency between NM and Rnq1 aggregates. The appearance of [PSI⁺] could be induced very efficiently even with a low expression level of the fusion protein. This study supports the in vivo cross-seeding between Sup35 and Rnq1 and provides a new tool that can be used to dissect the mechanism of the de novo appearance of prions.

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