Dbf4 Zn-finger motif is specifically required for stimulation of Ctf19-activated origins in S. cerevisiae

Eukaryotic genomes are replicated in spatiotemporal patterns that are stereotypical for individual genomes and developmental profiles. In the model system S. cerevisiae, two primary mechanisms determine the preferential activation of replication origins during early S phase, thereby largely defining the consequent replication profiles of these cells. Both mechanisms are thought to act through specific recruitment of a rate-limiting initiation factor, Dbf4-dependent kinase (DDK), to a subset of licensed replication origins. Fkh1/2 is responsible for stimulation of most early-firing origins, except for centromere (CEN)-proximal origins that recruit DDK via the kinetochore protein Ctf19, which is required for their early-firing. The C-terminus of Dbf4 has been implicated in its recruitment to origins via both the Fkh1/2 and Ctf19 mechanisms. Here, we show that the Zn-finger motif within the C-terminus is specifically required for Dbf4 recruitment to CENs to stimulate CEN-proximal/Ctf19-dependent origins, whereas stimulation of origins via the Fkh1/2 pathway remains largely intact. These findings re-open the question of exactly how Fkh1/2 and DDK act together to stimulate replication origin initiation.真核基因组的复制遵循兼具个体基因组特异性与发育谱特征的时空模式。在模式生物酿酒酵母（S. cerevisiae）中，两种核心机制决定了S期早期复制起点的优先激活事件，进而在很大程度上定义了这类细胞的后续复制图谱。目前认为，两种机制均通过将限速起始因子——依赖Dbf4的激酶（DDK）特异性招募至部分已获许可的复制起点来发挥作用。Fkh1/2负责激活绝大多数早激活复制起点，仅着丝粒（CEN）邻近的复制起点除外：这类起点通过动粒蛋白Ctf19招募DDK，而该过程是其早激活特性的必要条件。已有研究证实，Dbf4的C端参与介导通过Fkh1/2与Ctf19两种机制实现的起点招募。本研究表明，Dbf4 C端的锌指基序仅在Dbf4招募至着丝粒以激活着丝粒邻近/Ctf19依赖型复制起点时是必需的，而通过Fkh1/2通路激活复制起点的过程则基本不受影响。上述发现重新提出了一个关键科学问题：Fkh1/2与DDK究竟如何协同作用以调控复制起点的起始激活过程。