TIF1 represses rDNA replication initiation, but promotes normal S phase progression and chromosome transmission in Tetrahymena
TIF1 represses rDNA replication initiation, but promotes normal S phase progression and chromosome transmission in Tetrahymena
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DOI：
10.1091/mbc.e05-02-0107
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发表时间：
2005-06-01
影响因子：
3.3
通讯作者：
Kapler, GM
中科院分区：
文献类型：
--
作者：
Morrison, TL;Yakisich, JS;Kapler, GM
非ORC蛋白TIF 1识别嗜热四膜虫核糖体DNA（rDNA）微型染色体中的序列，这些序列是起源激活所需的。我们在这里表明，TIF 1抑制rDNA起源射击，但需要适当的大核S期进展和分裂。TIF 1突变体表现出延长的大核S期和降低的DNA复制速率。尽管如此，rDNA微型染色体的复制开始早熟。由于rDNA拷贝数在多倍体大核中不受影响，因此防止再起始的机制似乎是完整的。虽然突变体退出大核S与野生型的DNA含量，分裂的无丝分裂大核都延迟和异常。在二倍体有丝分裂微核中也观察到核缺陷，因为TIF 1突变体丢失了显著部分的微核DNA。因此，TIF 1是生殖系染色体繁殖和随后传递所必需的。与TIF 1缺陷相关的广泛表型表明，在S期和可能在细胞周期的后期阶段，这种起源结合蛋白是全球正确执行和/或监测关键染色体事件所必需的。我们提出，微观和大核缺陷的结果退出各自的核S期与物理受损的染色体。
The non-ORC protein, TIF1, recognizes sequences in the Tetrahymena thermophila ribosomal DNA (rDNA) minichromosome that are required for origin activation. We show here that TIF1 represses rDNA origin firing, but is required for proper macronuclear S phase progression and division. TIF1 mutants exhibit an elongated macronuclear S phase and diminished rate of DNA replication. Despite this, replication of the rDNA minichromosome initiates precociously. Because rDNA copy number is unaffected in the polyploid macronucleus, mechanisms that prevent reinitiation appear intact. Although mutants exit macronuclear S with a wild-type DNA content, division of the amitotic macronucleus is both delayed and abnormal. Nuclear defects are also observed in the diploid mitotic micronucleus, as TIF1 mutants lose a significant fraction of their micronuclear DNA. Hence, TIF1 is required for the propagation and subsequent transmission of germline chromosomes. The broad phenotypes associated with a TIF1-deficiency suggest that this origin binding protein is required globally for the proper execution and/or monitoring of key chromosomal events during S phase and possibly at later stages of the cell cycle. We propose that micro- and macronuclear defects result from exiting the respective nuclear S phases with physically compromised chromosomes.