FIG. 2.

Stability and curability of the USA⁺ phenotype. Strains expressing URE2-21, -22, -23, and -25 form stable, curable USA⁺ colonies. USA⁺ colonies from strains expressing the URE2 variants were streaked for single colonies onto YPAD and YPAD with 5 mM guanidine HCl. Single colonies were taken from the YPAD plate (+) and from YPAD plus guanidine (cured) and streaked on ammonia medium with uracil (right) or with USA (left) to test for the ability to utilize USA. The [ure-o] parent was included as a negative control (−).