cDNA encoding a human homolog of yeast ubiquitin 1

Ubiquitin is a highly conserved 76 residue protein apparently present in all eukaryotic cells. The protein forms an isopeptide link via its C-terminal alpha-carbo:;yl group to protein amino groups, and has been implicated in a variety of cellular -functions including regulation of actively transcribed genes (1) and non—lysosomal intracel1ular proteolysis (2). When screening a human U937 cDNA library -for cystatin A, by the procedures described in re-f. 3, we -fortuitously isolated the •following clone that encodes residues 40-76 of ubiquitin plus a C-terminal extension that exhibits 83Z identity with a similar gene -from Sacchargmyces cerevi_si_ae (4). This clone is closely related to a mouse cDNA (5) that probably represents a 3' truncated sequence. The arrow marks the beginning of the C-terminal extension, and the boxed and underlined residues respectively represent a putative DNA binding motif and nuclear translocation signal as suggested in ref. 4.