Enzymatic Expression and Genetic Linkage of Genes Controlling Galactose Utilization in Saccharomyces.

Mutations in our breeding stocks of Saccharomyces that produce the galactosenegative phenotype by blocking specific steps in this reaction sequence are gal, which affects the activity of galactokinase ( ROBICHON-SZULMAJSTER 1958) and gu,, which affects the activity of phosphoglucomutase (DOUGLAS 1961). Other mutations also affect the galactose phenotype of yeast. The transport of galactose into the cell is affected in gu, mutants (DOUGLAS and CONDIE 1954, ROBICHON-SZULMAJSTER 1961 ) while the phenotype of long-term adaption to galactose (WINGE and ROBERTS 1948; SPIEGELMAN, SUSSMAN, and PINSKA 1950) is a consequence of the gu, mutation. Suppression of the gu, phenotype is brought about by the recessive mutation iwhich allows constitutive synthesis of galactokinase, transferase and epimerase (DOUGLAS and PELROY 1963). The present work concerns the roles of the mutations ga,, gu,, and gal" in the galactose pathway, and the linkage relationships of the galactose genes. Evidence will be presented to show that gu7 and gal" block the synthesis of transferase and epimerase, respectively, and that gu4 prevents the synthesis of all three of the