Division of Microbial Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan.
Curr Biol. 2011 Dec 20;21(24):2055-63. doi: 10.1016/j.cub.2011.11.038. Epub 2011 Dec 8.
Chromosomal DNA replication in eukaryotes initiates from multiple origins of replication, and because of this multiplicity, activation of replication origins is likely to be highly coordinated; origins fire at characteristic times, with some origins firing on average earlier (early-firing origins) and others later (late-firing origins) in the S phase of the budding yeast cell cycle. However, the molecular basis for such temporal regulation is poorly understood.
We show that origin association of the low-abundance replication proteins Sld3, Sld7, and Cdc45 is the key to determining the temporal order of origin firing. These proteins form a complex and associate with the early-firing origins in G1 phase in a manner that depends on Dbf4-dependent kinase (DDK), which is essential for the initiation of DNA replication. An increased dosage of Sld3, Sld7, and Cdc45 allows the late-firing origins to fire earlier in S phase. Additionally, an increased dosage of DDK also allows the late-firing origins to fire earlier.
The DDK-dependent limited association between origins and Sld3-Sld7-Cdc45 is a key step for determining the timing of origin firing.
真核生物的染色体 DNA 复制从多个复制起点起始，由于这种多样性，复制起点的激活很可能是高度协调的；起点在特征时间被激活，一些起点在芽殖酵母细胞周期的 S 期平均更早（早期起点），而其他起点更晚（晚期起点）。然而，这种时间调节的分子基础知之甚少。
我们表明，低丰度复制蛋白 Sld3、Sld7 和 Cdc45 的起点关联是决定起点激活时间顺序的关键。这些蛋白质形成一个复合物，并以依赖 Dbf4 依赖性激酶（DDK）的方式与 G1 期的早期起点关联，DDK 对 DNA 复制的起始至关重要。Sld3、Sld7 和 Cdc45 的剂量增加允许晚期起点在 S 期更早地激活。此外，DDK 的剂量增加也允许晚期起点更早地激活。
DDK 依赖性起点与 Sld3-Sld7-Cdc45 之间的有限关联是决定起点激活时间的关键步骤。
