Figure 1.

Mutant strain SV16 contains a recessive, Mendelian mutation that weakens the nonsense suppression of [PSI+]. (A) Fivefold serial dilutions of indicated yeast cultures at equal cell density were spotted onto YPD, SD-ade, and YPD containing 3 mM GdnHCl. s[PSI+] and w[PSI+], strong and weak [PSI+] strains, respectively. (B) Spotting of [psi−], SV16, and the wild-type [psi−] × SV16 diploid on YPD, SD-ade, and YPD containing 3 mM GdnHCl (top). Two representative tetrads from sporulation of the wild-type [psi−] × SV16 diploid are shown (bottom). Asterisks denote spores that inherited the mutant allele.