Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.
Mol Biol Cell. 2010 May 15;21(10):1753-62. doi: 10.1091/mbc.e09-12-1079. Epub 2010 Mar 31.
Transposons comprise large fractions of eukaryotic genomes and provide genetic reservoirs for the evolution of new cellular functions. We identified TPB2, a homolog of the piggyBac transposase gene that is required for programmed DNA deletion in Tetrahymena. TPB2 was expressed exclusively during the time of DNA excision, and its encoded protein Tpb2p was localized in DNA elimination heterochromatin structures. Notably, silencing of TPB2 by RNAi disrupts the final assembly of these heterochromatin structures and prevents DNA deletion to occur. In vitro studies revealed that Tpb2p is an endonuclease that produces double-strand breaks with four-base 5' protruding ends, similar to the ends generated during DNA deletion. These findings suggest that Tpb2p plays a key role in the assembly of specialized DNA elimination chromatin architectures and is likely responsible for the DNA cleavage step of programmed DNA deletion.
转座子占据真核生物基因组的很大一部分，为新的细胞功能进化提供了遗传库。我们鉴定了 TPB2，它是一种必需的同源物，在四膜虫中参与程序性 DNA 缺失。TPB2 仅在 DNA 切除时表达，其编码的蛋白质 Tpb2p 定位于 DNA 消除异染色质结构中。值得注意的是，通过 RNAi 沉默 TPB2 会破坏这些异染色质结构的最终组装，并阻止 DNA 缺失的发生。体外研究表明，Tpb2p 是一种内切酶，它产生带有四碱基 5'突出端的双链断裂，类似于 DNA 缺失过程中产生的末端。这些发现表明，Tpb2p 在组装专门的 DNA 消除染色质结构中发挥关键作用，可能负责程序性 DNA 缺失的 DNA 切割步骤。
