Pleiotropic mutations regulating resistance to glucose repression in Saccharomyces carlsbergensis are allelic to the structural gene for hexokinase B.

Previously, we described a mutation glr1-1 in Saccharomyces carlsbergensis which pleiotropically relieves the synthesis of the following enzymes from glucose repression: maltase, galactokinase, alpha-galactosidase, NADH:cytochrome c reductase, and cytochrome c oxidase (C. A. Michels and A. Romanowski, J. Bacteriol, 143:674-679, 1980.) In this report, we demonstrate that glr1-1 and two other alleles, glr1-3 and glr1-16, are also insensitive to the glucose repression of invertase synthesis. Determinations of the levels of hexokinase activity and the rate of glucose transport in these mutants show that both are reduced as compared with the parent strain. Complementation tests and genetic analysis indicate that the glr1 mutations are allelic to HXK2, the structural gene for hexokinase B. The significance of this result is discussed with regard to the mechanism of glucose repression in S. carlsbergensis.