GALACTOKINASE ENCODED BY GAL1 IS A BIFUNCTIONAL PROTEIN REQUIRED FOR INDUCTION OF THE GAL GENES IN KLUYVEROMYCES-LACTIS AND IS ABLE TO SUPPRESS THE GAL3 PHENOTYPE IN SACCHAROMYCES-CEREVISIAE

We have analyzed a GAL1 mutant (gall-r strain) of the yeast Kluyveromyces lactis which lacks the induction of beta-galactosidase and the enzymes of the Leloir pathway in the presence of galactose. The data show that the K. lactis GAL1 gene product has, in addition to galactokinase activity, a function required for induction of the lactose system. This regulatory function is not dependent on galactokinase activity, as it is still present in a galactokinase-negative mutant (gall-209). Complementation studies in Saccharomyces cerevisiae show that K. lactis GAL1 and gall-209, but not gall-r, complement the gal3 mutation. We conclude that the regulatory function of GAL1 in K. lactis soon after induction is similar to the function of GAL3 in S. cerevisiae.