Table 1. The GuHCl test confirms facilitation of [PSI⁺] induction by Ht exon 1.

	No. of Ade+ colonies
Construct	Total tested	[PSI+]	[PSI+], %
Vector	17	8	47
Q25	17	9	53
Q47	14	9	64
Q72	8	7	88
Q103	28	27	96

Ade⁺ colonies from [rnq^-] transformants shown in Fig. 1 were transiently grown on YPD plus 5 mM GuHCl and were then scored for retention of suppression on media without GuHCl. Because some suppressors cause a transient change of color in GuHCl (53), cells were considered to have been [PSI⁺] only if they remained red following growth on GuHCl. Note that occasional [PSI⁺] colonies found among the rare Ade⁺ colonies in cultures carrying the empty vector, Q25, or Q47 constructs (see Fig. 1) probably reflect the spontaneous appearance of [RNQ⁺] (see ref. 15).