The MIG1 gene was disrupted in a haploid laboratory strain (B224) and in an industrial
polyploid strain (DGI 342) of Saccharomyces cerevisiae. The alleviation of
glucose repression of the expression of MAL genes and alleviation of
glucose control of
maltose metabolism were investigated in batch cultivations on
glucose-
maltose mixtures. In the MIG1-disrupted haploid strain,
glucose repression was partly alleviated; i.e.,
maltose metabolism was initiated at higher
glucose concentrations than in the corresponding wild-type strain. In contrast, the
polyploid delta mig1 strain exhibited an even more stringent
glucose control of
maltose metabolism than the corresponding wild-type strain, which could be explained by a more rigid catabolite inactivation of
maltose permease, affecting the uptake of
maltose. Growth on the
glucose-
sucrose mixture showed that the polypoid delta mig1 strain was relieved of
glucose repression of the SUC genes. The disruption of MIG1 was shown to bring about pleiotropic effects, manifested in changes in the pattern of secreted metabolites and in the specific growth rate.