Genetic Criteria for Yeast Prions

We use the word prion to mean an infectious protein, a protein that is altered in some way so that it does not carry out its normal function properly, but has acquired the ability to convert the normal form of the protein to the same abnormal (nonfunctional) form. By this definition, three properties are expected of a prion that are in contrast to the corresponding properties of a nucleic acid replicon (Wickner, 1994). 

If a yeast virus or plasmid (or the mitochodrial DNA genome) is cured from a strain, they will not return or arise again unless they are 

Properties that Distinguish Chromosomal Genes from Nonchromosomal Genes 

Induced loss of the gene Efficient curing by nonmuta-genic agents Induced mutation is still a rare event 

Mitotic segregation of alleles High frequency Low frequency 

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