Department of Biochemistry and Molecular Genetics, University of Illinois, Chicago, Illinois 60607, USA.
J Biol Chem. 2010 Feb 19;285(8):5327-37. doi: 10.1074/jbc.M109.078840. Epub 2009 Dec 29.
When the telomerase catalytic subunit (Trt1/TERT) is deleted, a majority of fission yeast cells survives by circularizing chromosomes. Alternatively, a small minority survives by maintaining telomeric repeats through recombination among telomeres. The recombination-based telomere maintenance in trt1Delta cells is inhibited by the telomere protein Taz1. In addition, catalytically inactive full-length Trt1 (Trt1-CI) and truncated Trt1 lacking the T-motif and reverse transcriptase (RT) domain (Trt1-DeltaT/RT) can strongly inhibit recombination-based survival. Here, we investigated the effects of deleting the heterochromatin proteins Swi6 (HP1 ortholog) and Clr4 (Suv39 family of histone methyltransferases) and the telomere capping complex subunits Poz1 and Ccq1 on Taz1- and Trt1-dependent telomere recombination inhibition. The ability of Taz1 to inhibit telomere recombination did not require Swi6, Clr4, Poz1, or Ccq1. Although Swi6, Clr4, and Poz1 were dispensable for the inhibition of telomere recombination by Trt1-CI, Ccq1 was required for efficient telomere recruitment of Trt1 and Trt1-CI-dependent inhibition of telomere recombination. We also found that Swi6, Clr4, Ccq1, the checkpoint kinase Rad3 (ATR ortholog), and the telomerase regulatory subunit Est1 are all required for Trt1-DeltaT/RT to inhibit telomere recombination. However, because loss of Swi6, Clr4, Rad3, Ccq1, or Est1 did not significantly alter the recruitment efficiency of Trt1-DeltaT/RT to telomeres, these factors are likely to enhance the ability of Trt1-DeltaT/RT to inhibit recombination-based survival by contributing to the negative regulation of telomere recombination.
当端粒酶催化亚基 (Trt1/TERT) 缺失时，大多数裂殖酵母细胞通过染色体环化存活。或者，一小部分通过端粒之间的重组来维持端粒重复序列存活。在 trt1Δ 细胞中，基于重组的端粒维持被端粒蛋白 Taz1 抑制。此外，无催化活性的全长 Trt1（Trt1-CI）和缺乏 T 基序和逆转录酶（RT）结构域的截短 Trt1（Trt1-DeltaT/RT）可以强烈抑制基于重组的存活。在这里，我们研究了删除异染色质蛋白 Swi6（HP1 同源物）和 Clr4（组蛋白甲基转移酶 Suv39 家族）以及端粒加帽复合物亚基 Poz1 和 Ccq1 对 Taz1 和 Trt1 依赖性端粒重组抑制的影响。Taz1 抑制端粒重组的能力不需要 Swi6、Clr4、Poz1 或 Ccq1。虽然 Swi6、Clr4 和 Poz1 对于 Trt1-CI 抑制端粒重组是可有可无的，但 Ccq1 对于 Trt1 和 Trt1-CI 依赖性端粒重组抑制的有效端粒募集是必需的。我们还发现，Swi6、Clr4、Ccq1、检查点激酶 Rad3（ATR 同源物）和端粒酶调节亚基 Est1 都需要 Trt1-DeltaT/RT 抑制端粒重组。然而，由于缺失 Swi6、Clr4、Rad3、Ccq1 或 Est1 并没有显著改变 Trt1-DeltaT/RT 向端粒的募集效率，这些因素可能通过促进端粒重组的负调控来增强 Trt1-DeltaT/RT 抑制基于重组的存活的能力。
