Regulation of maltose transport in Saccharomyces cerevisiae T.H.C. Brondijk, M.E. van der Rest, B. Poolman and W.N.Konings University of Groningen, The Netherlands Following the addition of glucose to maltose metabolizing cells of Saccharomyces cerevisiae, the transport of maltose is rapidly slowed down. The mechanism of inactivation of the maltose transport protein (catabolite inactivation) is studied. Genetically well-defined S. cerevisiae strains have been constructed that only express a single maltose transporter (MAL11 or MAL61). Potential phosphorylation sites in MAL61p have been mutated. One of the putative phosphorylation site mutants studied, thus far, has a reduced rate of catabolite inactivation. To study the control of the maltose transporter on metabolic fluxes, a S. cerevisiae strain has been constructed that expresses maltase under control of the constitutive alcohol dehydrogenase promotor. In this strain the MAL61 gene has been expressed under control of the galactose inducible promoter. The level of MAL61p has been varied by induction with different concentrations of galactose and/or using different induction times. The initial maltose uptake capacity in these cultures is compared with the real maltose uptake and ethanol/CO2 production.