Yamada M, Hayatsu N, Matsuura A, Ishikawa F
Department of Life Science, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
J Biol Chem. 1998 Dec 11;273(50):33360-6. doi: 10.1074/jbc.273.50.33360.
The yeast Y' element is a highly polymorphic repetitive sequence present in the subtelomeric regions of many yeast telomeres. The Y' element is classed as either Y'-L or Y'-S, depending on its length. It has been reported that survivors arising from telomerase-deficient yeast mutants compensate for telomere loss by the amplification of Y' elements. The total Saccharomyces cerevisiae genome DNA data base was searched for Y' elements, and 11 Y'-Ls and eight Y'-Ss were identified. As reported previously, many of the sequences were found to contain long open reading frames which potentially encode helicase. We examined the expression of the Y' elements in telomerase-deficient Deltatlc1 survivors, in which the TLC1 gene encoding the yeast telomerase template RNA had been disrupted, and found that the Y' element is highly expressed in the survivors, but not in the wild-type cells. Moreover, we demonstrated that the survivors produce a Y'-encoded protein designated as Y'-Help1 (Y'-helicase protein 1), and that this protein possesses helicase activity. Therefore, we suggest that the Y' element has a novel and potentially important role in trans, in addition to the well characterized role in cis, in telomerase-independent telomere maintenance in yeast.
酵母Y'元件是一种高度多态的重复序列，存在于许多酵母端粒的亚端粒区域。根据其长度，Y'元件可分为Y'-L或Y'-S。据报道，端粒酶缺陷型酵母突变体产生的存活者通过Y'元件的扩增来补偿端粒丢失。在酿酒酵母全基因组数据库中搜索Y'元件，共鉴定出11个Y'-L和8个Y'-S。如先前报道，许多序列含有可能编码解旋酶的长开放阅读框。我们检测了端粒酶缺陷型Δtlc1存活者中Y'元件的表达，其中编码酵母端粒酶模板RNA的TLC1基因已被破坏，发现Y'元件在存活者中高度表达，而在野生型细胞中不表达。此外，我们证明存活者产生一种由Y'编码的蛋白质，命名为Y'-Help1（Y'-解旋酶蛋白1），并且这种蛋白质具有解旋酶活性。因此，我们认为Y'元件除了在顺式中对酵母中端粒酶非依赖性端粒维持具有已明确的作用外，在反式中还具有新的潜在重要作用。
