Aspartokinase (EC 2.7.2.4) is encoded by the HOM3 gene, a putative clone of which was previously isolated on a recombinant plasmid pSC3 (15.5 kbp) by its HOM3 complementing ability in the yeast localized to the 2.15 kbp BamHI-BgIII fragment by subcloning it from the pSC3. A replicating vector YRp7 to yield the plasmid pSC35. In an attempt to yield the integrative plasmid pSC351, the EcoRI fragment containing ARS-TRP1 was removed from pSC35. Mitotically stable integrative transformants were stable integrative transformants were selected upon introducing the linearized pSC351 into the original yeast recipient strain and crossed with an appropriate yeast strain for tetrad analysis. As a result, the integrated pSC351 DNA was positioned to the expected genetic distance of 3.9 cM from the HIS1 locus on the right arm of yeast chromosome V, indicating that the 2.15 kbp fragment in pSC35 contains the entire functional HOM3 gene of the yeast, Saccharomyces cerevisiae.