Table 7.

Mutations in the CH domain or the helicase region of Upf1p can impair elimination of Upf1p-sensitive [PSI+] variants

UPF1 alleles in plasmid	Average % Ura+ transformant clones, ± SD	Phenotype of subclones from Ura− clones that lost plasmid
		Ura+	Ura−
Vector	99.9 ± 0.1a
pUPF1-WT	4.7 ± 1.4b	2	114
pUPF1-C62Y	92.4 ± 3.5c	1	84
pUPF1-C72S	2.5 ± 2.2b	0	109
pUPF1-C84S	90.7 ± 5.7c	1	97
pUPF1-C125S	86.1 ± 3.3c	0	88
pUPF1-K436Q	70.4 ± 7.1d	1	121
pUPF1-DE572AA	71.8 ± 2.9d	1	94
pUPF1-TR800AA	68.2 ± 4.5d	1	113
pUPF1-RR793AA	51.9 ± 2.0e	0	78
pUPF1-RR793KK	4.4 ± 1.0b	0	81

Primary [PSI+u1s] upf1Δ isolates (MS2, MS5, and MS6) and three other [PSI+u1s] isolated in the upf1Δ strain MS114 (MS318, MS319, and MS320) were transformed with the CEN vector pRS313 or the vector carrying UPF1 (pM25) or UPF1 mutated by amino acid substitution(s) under its native promoter. Substituted amino acid(s) and their positions are shown. Transformants were selected in the presence of uracil and were replica-plated to a plate lacking uracil. More than 400 transformant clones were investigated in each case. The average percent of Ura⁺ transformants, calculated using six independent experiments, ± SD, is shown. Numbers with different letters are significantly different at a P value of <0.05 based on the Tukey test. Ura⁻ subclones that had lost each plasmid were tested for uracil auxotrophy by replica-plating. Their failure to become Ura⁺ again shows that the prion was cured.