Agell N, Bond U, Schlesinger M J
Department of Microbiology and Immunology, Washington University School of Medicine, Saint Louis, MO 63110.
Proc Natl Acad Sci U S A. 1988 Jun;85(11):3693-7. doi: 10.1073/pnas.85.11.3693.
Ubiquitin, a highly conserved protein of 76 amino acids found in all eukaryotes, is translated from mRNAs that contain either multiple, contiguous coding sequences of the protein or a single ubiquitin coding sequence fused to sequences coding for 52 or 76 amino acids. We describe here formation of monoubiquitin from in vitro translation of mRNAs containing either two complete sequences or one complete ubiquitin and 60% of a second ubiquitin. No diubiquitin precursor was found with the complete diubiquitin mRNA, but the truncated mRNA formed proteins with apparent molecular masses of 30, 24, 7, and 4 kDa. The latter two are the expected products from truncated ubiquitin mRNA. The 30-kDa protein was immunoprecipitated by anti-ubiquitin antibodies and was converted to ubiquitin and the 4-kDa form by a ubiquitin isopeptidase-like activity in wheat germ. Other data indicated that the 30-kDa protein had multiple ubiquitins, all linked by isopeptide bonds to the truncated ubiquitin. One of these was the radiolabeled translation product, which should have been linked to the truncated protein by a normal peptide bond. A model is proposed in which ubiquitin itself participates in a transpeptidase activity.
泛素是一种在所有真核生物中都存在的由76个氨基酸组成的高度保守的蛋白质，它由含有该蛋白质多个连续编码序列的mRNA或与编码52或76个氨基酸的序列融合的单个泛素编码序列翻译而来。我们在此描述了通过体外翻译含有两个完整序列或一个完整泛素和第二个泛素60%的mRNA形成单泛素的过程。在完整的双泛素mRNA中未发现双泛素前体，但截短的mRNA形成了表观分子量为30、24、7和4 kDa的蛋白质。后两者是截短的泛素mRNA的预期产物。30 kDa的蛋白质被抗泛素抗体免疫沉淀，并通过小麦胚芽中的一种泛素异肽酶样活性转化为泛素和4 kDa的形式。其他数据表明，30 kDa的蛋白质有多个泛素，它们都通过异肽键与截短的泛素相连。其中一个是放射性标记的翻译产物，它应该通过正常的肽键与截短的蛋白质相连。提出了一个模型，其中泛素本身参与转肽酶活性。
