Toxicity of 2-deoxygalactose to Saccharomyces cerevisiae cells constitutively synthesizing galactose-metabolizing enzymes.

Analysis of 400 independent spontaneous mutations conferring 2-deoxygalactose resistance upon cells constitutive for the galactose pathway suggests that toxicity is due to 2-deoxygalactose-1-phosphate. Selection for and against growth on galactose in the same strain is now possible; application to systems with transcriptional or translational gene fusions to galactokinase are discussed.