Royzman I, Austin R J, Bosco G, Bell S P, Orr-Weaver T L
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142 USA.
Genes Dev. 1999 Apr 1;13(7):827-40. doi: 10.1101/gad.13.7.827.
We isolated mutations in Drosophila E2F and DP that affect chorion gene amplification and ORC2 localization in the follicle cells. In the follicle cells of the ovary, the ORC2 protein is localized throughout the follicle cell nuclei when they are undergoing polyploid genomic replication, and its levels appear constant in both S and G phases. In contrast, when genomic replication ceases and specific regions amplify, ORC2 is present solely at the amplifying loci. Mutations in the DNA-binding domains of dE2F or dDP reduce amplification, and in these mutants specific localization of ORC2 to amplification loci is lost. Interestingly, a dE2F mutant predicted to lack the carboxy-terminal transcriptional activation and RB-binding domain does not abolish ORC2 localization and shows premature chorion amplification. The effect of the mutations in the heterodimer subunits suggests that E2F controls not only the onset of S phase but also origin activity within S phase.
我们在果蝇E2F和DP中分离出了影响绒毛膜基因扩增和卵泡细胞中ORC2定位的突变。在卵巢的卵泡细胞中，当卵泡细胞核进行多倍体基因组复制时，ORC2蛋白定位于整个卵泡细胞核，并且其水平在S期和G期似乎保持恒定。相比之下，当基因组复制停止且特定区域扩增时，ORC2仅存在于扩增位点。dE2F或dDP的DNA结合结构域中的突变会减少扩增，并且在这些突变体中，ORC2到扩增位点的特异性定位丧失。有趣的是，一个预测缺乏羧基末端转录激活和RB结合结构域的dE2F突变体并没有消除ORC2定位，而是显示出过早的绒毛膜扩增。异二聚体亚基中突变的影响表明，E2F不仅控制S期的起始，还控制S期内的起始活性。
