Use of sulfite resistance in Saccharomyces cerevisiae as a dominant selectable marker

Two S. cerevisine genes were found to exhibit dominant phenotypes useful fo r selecting transformants of industrial and laboratory strains of S. cerevi sine. FZF1-4, which confers sulfite resistance, was originally isolated and identified as RSU1-4, but the two genes are shown here to be allelic. Cyst eine 57 in wild-type Fzf1p was found to be replaced by tyrosine in Fzfl-4p. Multicopy SSU1, which also confers sulfite resistance, was found to be som ewhat less efficient. In both cases, a period of outgrowth in non-selective medium following transformation was found to be necessary. The number of t ransformants obtained was found to be strain-dependent, and also to depend on the sulfite concentration used during selection. Undesirable background growth of non-transformants was not observed at cell densities as high as 2 .5 x 10(7)/plate. In two ura3 laboratory strains where selection for URA3 w as applied independently of that for sulfite, the transformation efficiency for sulfite resistance was about 50% that for uracil prototrophy.