Ubiquitin is a polypeptide consisting of 76 amino acid residues and is present in all eukaryotes studied so far. It is one of the most highly conserved proteins known, differing at only 4 of 76 positions in such diverse organisms as yeast, maize, and human (Callis and Vierstra, 1989). The protein has been implicated in many vital cellular processes, such as protein turnover (Hershko, 1988), cell cycle control (Rechsteiner, 1991), response to heat shock, and resistance to heavy metal (Bond and Schlesinger, 1986; Jungmann et al., 1993). We report here the isolation and sequence determination of a genomic DNA that encodes a polyubiquitin in soybean (Glycine max L. Merr.). Soybean leaf genomic DNA was partially digested with Sau3AI and used to construct a library in BamHI-digested XEMBL3. Putative positive clones containing ubiquitin genes were isolated from the genomic DNA library, using a 1.1-kb EcoRI/HindIII fragment of the soybean cDNA clone pUBS6 (Fortin et al., 1988) as a probe. Thirteen positive plaques were identified by plaque hybridization and, after DNA preparation, the inserts of the 13 clones were subcloned into plasmid vector Bluescript II SK+. On the basis of restriction maps and hybridization data, the 13 genome clones could be divided into three types (data not shown). One of the clones, pSUB38 (Table I), was sequenced by a modified version of the dideoxy-chain termination method using an Applied Biosystems model 370 Sequencer. This soybean genomic DNA clone contained an insert of 2309 bp, including a 915bp ORF. To analyze the promoter of the ubiquitin gene in the 5' noncoding region, the upstream fragment was also sequenced. The 915-bp ORF encoding polyubiquitin was arranged as three tandem, head-to-tail, 228-bp repeats and a fourth, terminal repeat containing 231 bp. This ORF encodes a polypeptide of 305 amino acid residues. The first three repeats contained 76 amino acid residues each, whereas the terminal repeat contained an additional Phe residue. This additional amino acid is presumably removed during processing of the polyubiquitin to the mature monomers (Chrislensen et al., 1992). The amino acid sequence deduced for soybean polyubi-