TABLE 2.

Effect of Ssb on the rates of spontaneous [PSI] formation in [psi⁻ PIN⁺] background

Strain	Frequency of Ade+ colonies		Rate of Ade+ appearance
	Median	95% confidence limit	Median	95% confidence limit
GT159 (Ssb+)	1.7 × 10−6	(1.0–3.5) × 10−6	7.3 × 10−7	(4.0–11.0) × 10−7
GT157 (Ssb−)	3.1 × 10−5	(1.5–3.5) × 10−5	6.4 × 10−6	(3.3–7.2) × 10−6