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Artificial genes, which encode 48 or 64 repeats of a tripeptide, glutamyl–tryptophanyl–lysine have been cloned to the yeast expression vector pAM82 containing the PHO5 promoter and expressed in Saccharomyces cerevisiae AH22.When the yeast cells harbouring recombinant plasmids pALTG6-2 and pALTG4-4 were derepressed in Burkholder minimal medium (Toh-e, A., Ueda, Y., Kakimoto, S.I. and Oshima, Y. (1973) Journal of Bacteriology113, 727–738) containing low phosphate (0·03 g l−1 KH2PO4 and 1·5 g l−1 KCl), the expression was the highest after 24 h induction and the artificial polypeptides were synthesized to about 10% (pALTG6-2) and 14% (pALTG4-4) of the total cell protein.The artificial polypeptides produced in yeast were made to react with the rabbit antiserum against the polypeptide purified from Escherichia coli and found only in the pellet fraction of cell lysates, indicating the formation of inclusion body. Artificial polypeptide consisting of Glu–Trp–Lys may be useful as partial supplement in food and feeds.The production of single cell enriched with homopolymers of an essential amino acid in yeast might be an important tool of supplementing cereal diets and feed grain rations and could be used as means for improvement of the amino acid profile of single cell protein and production of pharmaceutical peptides.