FIG 1.

Mutations in Ure2 that impair [URE3] propagation. (A) Individual amino acid substitutions identified as causing Ure2 to impair [URE3] when expressed exogenously in wild-type cells are indicated at the top. Those shown in bold were characterized. (B) Examples of dominant inhibitory effects of Ure2 mutants on [URE3]. Wild-type [URE3] strain 1075 was transformed by plasmids encoding Ure2 with the indicated amino acid substitutions. Transformants were selected on plates containing limiting adenine, on which cells that have lost [URE3] grow faster and accumulate red pigment. Shown are 2.5-cm² sections of plates incubated for 3 days at 30°C followed by 2 days at 25°C. (C) Strain MR149 (ure2Δ) was transformed by empty vector (ev) or plasmids encoding wild-type (wt) and mutant (as indicated) Ure2 proteins. Shown are 2.5-cm² sections of transformation plates incubated for 3 days at 30°C. The extent of Ure2 function is reflected in the degree of red coloration. (D) Western analysis for abundance of Ure2 proteins (as indicated) in cells expressing Ure2 from the URE2 chromosomal locus. The panel labeled CB shows identically loaded gel stained with Coomassie blue dye.