Table 1.

Yeast prion variant classification.

Variant-Defining Condition/Trait	Prions Affected	Mechanism	Relation to Strong/Weak?	Refs.
Strength of phenotype (strong/weak)	[PSI+], [URE3]	high filament number adsorb more prion protein		[10,28,29]
Prion stability	[PSI+], [URE3]	high filament number insures both daughters infected	Strong often stable, weak often unstable; exceptions	[10,28,29]
prion toxicity (all variants detrimental but the degree varies)	[PSI+], [URE3]	[PSI+]: depletion of Sup35p (essential) [URE3]: toxic effect of amyloid form	unknown	[33]
interspecies or intraspecies barriers	[PSI+], [URE3]	inefficient binding to amyloid of different protein sequence		[34,35,36]
lethality or prion loss in Sis1p partial deletions	[PSI+]	unknown	strong variant lethal; weak variant lost	[37,38]
Sse1p required for propagation or generation	[PSI+]		strong variant weakened, weak variant lost	[39,40]
curing by normal levels of Hsp104	[PSI+]		some of both are cured; no relation to seed #	[41]
curing by normal levels of Btn2p	[URE3]	filaments sequestered by Btn1p, Hsp42p	All cured variants are weak, but some weak variants not cured	[42]
curing by normal levels of Cur1p	[URE3]	unknown	All cured variants are weak, but some weak variants not cured	[42]
curing by normal levels of Upf1,2,3	[PSI+]	complex formation with Sup35p	no relation to strong/weak	[43]
curing by normal levels of Siw14p	[PSI+]	limits 5PP-IP5 levels	unknown	[44]