Zielke Norman, Querings Silvia, Grosskortenhaus Ruth, Reis Tânia, Sprenger Frank
Institute for Genetics, University of Cologne, Zülpicherstrasse 47, 50674 Köln, Germany.
EMBO Rep. 2006 Dec;7(12):1266-72. doi: 10.1038/sj.embor.7400851. Epub 2006 Nov 10.
Rca1 (regulator of Cyclin A)/Emi (early mitotic inhibitor) proteins are essential inhibitors of the anaphase-promoting complex/cyclosome (APC/C). In Drosophila, Rca1 is required during G2 to prevent premature cyclin degradation by the Fizzy-related (Fzr)-dependent APC/C activity. Here, we present a structure and function analysis of Rca1 showing that a carboxy-terminal fragment is sufficient for APC/C inhibition. Rca1/Emi proteins contain a conserved F-box and interact with components of the Skp-Cullin-F-box (SCF) complex. So far, no function has been ascribed to this domain. We find that the F-box of Rca1 is dispensable for APC/C-Fzr inhibition during G2. Nevertheless, we show that Rca1 has an additional function at the G1-S transition, which requires the F-box. Overexpression of Rca1 accelerates the G1-S transition in an F-box-dependent manner. Conversely, S-phase entry is delayed in cells in which endogenous Rca1 is replaced by a transgene lacking the F-box. We propose that Rca1 acts as an F-box protein in an as yet uncharacterized SCF complex, which promotes S-phase entry.
Rca1（细胞周期蛋白A调节因子）/Emi（早期有丝分裂抑制剂）蛋白是后期促进复合体/细胞周期体（APC/C）的重要抑制剂。在果蝇中，G2期需要Rca1来防止Fizzy相关蛋白（Fzr）依赖的APC/C活性过早降解细胞周期蛋白。在此，我们展示了Rca1的结构和功能分析，表明其羧基末端片段足以抑制APC/C。Rca1/Emi蛋白含有一个保守的F盒，并与Skp-Cullin-F盒（SCF）复合体的组分相互作用。到目前为止，该结构域尚未被赋予任何功能。我们发现，Rca1的F盒在G2期对APC/C-Fzr的抑制作用中是可有可无的。然而，我们表明Rca1在G1-S期转换时具有额外功能，这需要F盒。Rca1的过表达以F盒依赖的方式加速G1-S期转换。相反，在内源Rca1被缺乏F盒的转基因取代的细胞中，S期进入延迟。我们提出，Rca 在一个尚未明确的SCF复合体中作为F盒蛋白发挥作用，促进S期进入。
