Genes are disclosed which are capable of directing the synthesis in a selected host microorganism of thaumatin I polypeptides having improved taste characteristics characterized by having the amino acid sequence of natural thaumatin I including a lysine amino acid residue substituted for asparagine in the 46th position from the amino terminal end, an aspartate amino acid residue substituted for asparagine in the 113th position from the amino terminal end and an aspartate amino acid residue substituted for lysine at either the 97th or 137th residue from the amino terminal end.
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