14 Aug 2002 14:0 AR AR168-MI56-28.tex AR168-MI56-28.sgm LaTeX2e(2002/01/18) P1: IBD 10.1146/annurev.micro.56.013002.100603 Annu. Rev. Microbiol. 2002. 56:703–41 doi: 10.1146/annurev.micro.56.013002.100603 Copyright c 2002 by Annual Reviews. All rights reserved First published online as a Review in Advance on July 15, 2002 PRIONS AS PROTEIN-BASED GENETIC ELEMENTS Susan M. Uptain1 and Susan Lindquist2 1Howard Hughes Medical Institute, Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637; e-mail:
[email protected] 2Whitehead Institute for Biomedical Research, Department of Biology, Massachusetts Institute of Biology, Nine Cambridge Center, Cambridge, Massachusetts 02142; e-mail: lindquist
[email protected] Key Words Sup35, Ure2, HET-s, Rnq1, amyloid ■ Abstract Fungal prions are fascinating protein-based genetic elements. They alter cellular phenotypes through self-perpetuating changes in protein conformation and are cytoplasmically partitioned from mother cell to daughter. The four prions of Saccharomyces cerevisiae and Podospora anserina affect diverse biological pro- cesses: translational termination, nitrogen regulation, inducibility of other prions, and heterokaryon incompatibility. They share many attributes, including unusual genetic behaviors, that establish criteria to identify new prions. Indeed, other fungal traits that baffled microbiologists meet some of these criteria and might be caused by prions. Recent research has provided notable insight about how prions are induced and prop- agated and their many biological roles. The ability to become a prion appears to be evolutionarily conserved in two cases. [PSI+] provides a mechanism for genetic vari- ation and phenotypic diversity in response to changing environments.