◎DE1 gene encodes a phosphoribosylamino imidazole succinocarboxylamide synthe◎ which converts phosphoribosylamino imidazole carboxylate to phosphoribosyl suc◎ocarboxamide aminoimidazole in de novo pathway of adenine biosynthesis. We cloned ◎DE1 gene by the complementation of ade1 mutation in yeast and localized ADE1 gene in cloned plasmid by constructing the several subcloned derivatives. There are two separate DNA fragments which are related to complement the ade1 mutation, the large DNA fragment designated as ADE_L1 and the smaller DNA fragment designated as ADE_S1. The restriction map of ADE_L1 gene exactly coincides with the restriction map of ADE1 gene analyzed by several group. However, the smaller DNA fragment seems to have a novel function involved in complementing ade1 mutation without ADE_L1 DNA fragment, but the recombinant plasmid carrying the ADE_S1 gene shows weaker transformability than that of ADE_L1 gene. To identify the role of the smaller DNA fragment in adenine biosynthesis, we determined its nucleotide sequence by the methods of dideoxy DNA sequencing with PUC plasmids derivatives.