Gong Tzy-Wen L, Huang Li, Warner Steven J, Lomax Margaret I
Kresge Hearing Research Institute, Department of Otolaryngology/Head-Neck Surgery, University of Michigan Medical School, Ann Arbor, MI 48109-0648, USA.
Genomics. 2003 Aug;82(2):143-52. doi: 10.1016/s0888-7543(03)00111-3.
E3 ubiquitin ligases target proteins for degradation by adding ubiquitin residues. We characterized full-length cDNAs for human and mouse UBE3B, a novel HECT-domain E3 ligase, and analyzed the structure of human UBE3B on chromosome 12q24.1. Alternative splicing of exon 20 of UBE3B generated two major transcripts. The 5.7-kb mRNA lacked exon 20 and encoded a full-length protein ligase, variant 1 (UBE3B_v1). A second transcript contained a 97-bp insertion encoded by exon 20 that introduced an in-frame stop codon. The predicted protein (UBE3B_v2) would lack the HECT domain and would be nonfunctional, since the HECT domain constitutes the active site for ubiquitin transfer. No alternative splicing was observed in this region of mouse UBE3B. Elimination of the HECT domain by alternative splicing has not been reported in any genes encoding HECT domain ligases and may represent a novel mechanism in regulating intracellular levels of functional HECT-domain ligases.
E3泛素连接酶通过添加泛素残基来靶向蛋白质进行降解。我们鉴定了人类和小鼠UBE3B（一种新型的含HECT结构域的E3连接酶）的全长cDNA，并分析了位于12q24.1染色体上的人类UBE3B的结构。UBE3B第20外显子的可变剪接产生了两种主要转录本。5.7 kb的mRNA缺少第20外显子，编码一种全长蛋白连接酶，即变体1（UBE3B_v1）。第二种转录本包含由第20外显子编码的97 bp插入片段，该片段引入了一个框内终止密码子。预测的蛋白质（UBE3B_v2）将缺少HECT结构域且无功能，因为HECT结构域构成了泛素转移的活性位点。在小鼠UBE3B的该区域未观察到可变剪接。通过可变剪接消除HECT结构域在任何编码HECT结构域连接酶的基因中均未报道过，这可能代表了一种调节功能性HECT结构域连接酶细胞内水平的新机制。
