A process for the production of a protein or peptide which is heterologous to yeast which comprises inducing the expression of the protein or peptide in a yeast, which has been genetically modified to be capable of expressing the heterologous protein or peptide upon induction by galactose, the induction being carried out in the presence of a galactose-containing medium which contains a significant amount of glucose, and obtaining the said heterologous protein or peptide therefrom.
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