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Published December 13, 1984 | public
Journal Article

The yeast ubiquitin gene: head-to-tail repeats encoding a polyubiquitin precursor protein


Ubiquitin, a 76-residue protein, occurs in cells either free or covalently joined to a variety of protein species, from chromosomal histones to cytoplasmic proteins. Conjugation of ubiquitin to proteolytic substrates is essential for the selective degradation of intracellular proteins in higher eukaryotes. We show here that a protein homologous to human ubiquitin exists in the yeast Saccharomyces cerevisiae, and that yeast extracts conjugate human ubiquitin to a variety of endogenous proteins in an ATP-dependent reaction. We have isolated the S. cerevisiae ubiquitin gene and found it to contain six consecutive ubiquitin-coding repeats in a head-to-tail arrangement. This apparently unique gene organization suggests that yeast ubiquitin is generated by processing of a precursor protein in which several exact repeats of the ubiquitin amino acid sequence are joined directly via Gly–Met peptide bonds between the last and first residues of mature ubiquitin, respectively. Ubiquitin-coding yeast DNA repeats are restricted to a single genomic locus; although the sequenced repeats differ in up to 27 of 228 bases per repeat, they encode identical amino acid sequences. As this predicted amino acid sequence differs in only 3 of 76 residues from that of ubiquitin in higher eukaryotes, ubiquitin is apparently the most conserved of known proteins.

Additional Information

© 1984 Nature Publishing Group. Received 12 September; accepted 15 October 1984. We thank Richard Young and Ronald Davis for the Agt11 library, Aaron Ciechanover for the anti-ubiquitin antibody, Jacqueline Whang for her assistance in some experiments, and Igor Roninson, Mark Solomon, Frans:ois Strauss, Paul Swerdlow and especially Joan Park and Lulu Pickering for technical advice and comments on the manuscript. We also thank Barbara Doran for secretarial assistance. This work was supported by grants to A.V. from the National Institute of General Medical Sciences (GM31530 and GM26086).

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