Inactivation of maltose permease and maltase in sporulating Saccharomyces cerevisiae

Maltose transport and maltase activities were inactivated during sporulatio n of a MAL constitutive yeast strain harboring different MAL loci. Both act ivities were reduced to almost zero after 5 h of incubation in sporulation medium. The inactivation of maltase and maltose permease seems to be relate d to optimal sporulation conditions such as a suitable supply of oxygen and cell concentration in the sporulating cultures, and occurs in the fully de repressed conditions of incubation in the sporulation acetate medium. The i nactivation of maltase and maltose permease under sporulation conditions in MAL constitutive strains suggests an alternative mechanism for the regulat ion of the MAL gene expression during the sporulation process.