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The Protein Product of the Het-s Heterokaryon Incompatibility Gene of the Fungus Podospora anserina Behaves as a Prion Analog

Virginie Coustou, Carol Deleu, Sven Saupe and Joel Begueret
Proceedings of the National Academy of Sciences of the United States of America
Vol. 94, No. 18 (Sep. 2, 1997), pp. 9773-9778
Stable URL: http://www.jstor.org/stable/43101
Page Count: 6
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The Protein Product of the Het-s Heterokaryon Incompatibility Gene of the Fungus Podospora anserina Behaves as a Prion Analog
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Abstract

The het-s locus of Podospora anserina is a heterokaryon incompatibility locus. The coexpression of the antagonistic het-s and het-S alleles triggers a lethal reaction that prevents the formation of viable heterokaryons. Strains that contain the het-s allele can display two different phenotypes, [Het-s] or [Het-s*], according to their reactivity in incompatibility. The detection in these phenotypically distinct strains of a protein expressed from the het-s gene indicates that the difference in reactivity depends on a posttranslational difference between two forms of the polypeptide encoded by the het-s gene. This posttranslational modification does not affect the electrophoretic mobility of the protein in SDS/PAGE. Several results suggest a similarity of behavior between the protein encoded by the het-s gene and prions. The [Het-s] character can propagate in [Het-s*] strains as an infectious agent, producing a [Het-s*] → [Het-s] transition, independently of protein synthesis. Expression of the [Het-s] character requires a functional het-s gene. The protein present in [Het-s] strains is more resistant to proteinase K than that present in [Het-s*] mycelium. Furthermore, overexpression of the het-s gene increases the frequency of the transition from [Het-s*] to [Het-s]. We propose that this transition is the consequence of a self-propagating conformational modification of the protein mediated by the formation of complexes between the two different forms of the polypeptide.

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