Stability of prions in cells expressing different SSA alleles

Straina:Prion loss (%)
([PSI+]/[URE3])SSA genotypeb[PSI+][URE3]
792/1075SSA1 SSA2<0.1<0.1
793/1079SSA1-21 SSA24.5 ± 1.8c<0.1
912/1082SSA1 SSA2-218.6 ± 2.5c11 ± 4
794/1076ssa1Δ SSA2<0.1<0.1
812/1080SSA1 ssa2Δ<0.17.8 ± 1.6
814/ssa1Δ ssa2Δ<0.1NA
/1085SSA1-21 ssa2ΔNA17 ± 3
1135/1161SSA1 only<0.115 ± 3
1135/1161SSA2 only<0.1<1
1135/1161SSA3 only<0.129 ± 4
1135/1161SSA4 only<1<1
/1161SSA1-21 onlyNA13 ± 3
  • Cells from white colonies on 1/2YPD were streaked or diluted in water and spread onto 1/2YPD plates and grown for 3 days at 30° followed by 5 days at 23°. Among a total of 250–1000 resulting colonies for each strain, entirely red colonies were scored as having lost the prion. Data are averages of 3–6 trials ± SE. SSA gene combinations that abolish propagation of both prions (i.e., SSA1-21 SSA2-21 and ssa1Δ SSA2-21) are not included on the table, and NA (not applicable) indicates where SSA gene combination does not allow propagation of one or the other prion.

  • a The slash between strain numbers distinguishes strains used to monitor [PSI+] (left of slash) and [URE3] (right of slash).

  • b Strains except 1135 and 1161 have indicated genes on chromosomes and have genomic SSA3 and SSA4. Strains 1135 and 1161 lack all four chromosomal SSA alleles and express the indicated SSA gene, driven by the SSA2 promoter, from a single-copy plasmid.

  • c Statistically, the values for these numbers overlap.