Vergés Emili, Colomina Neus, Garí Eloi, Gallego Carme, Aldea Martí
Departament de Ciències Mèdiques Bàsiques, IRBLLEIDA, Universitat de Lleida, Montserrat Roig 2, 25008 Lleida, Catalonia, Spain.
Mol Cell. 2007 Jun 8;26(5):649-62. doi: 10.1016/j.molcel.2007.04.023.
G1 cyclin Cln3 plays a key role in linking cell growth and proliferation in budding yeast. It is generally assumed that Cln3, which is present throughout G1, accumulates passively in the nucleus until a threshold is reached to trigger cell cycle entry. We show here that Cln3 is retained bound to the ER in early G1 cells. ER retention requires binding of Cln3 to the cyclin-dependent kinase Cdc28, a fraction of which also associates to the ER. Cln3 contains a chaperone-regulatory Ji domain that counteracts Ydj1, a J chaperone essential for ER release and nuclear accumulation of Cln3 in late G1. Finally, Ydj1 is limiting for release of Cln3 and timely entry into the cell cycle. As protein synthesis and ribosome assembly rates compromise chaperone availability, we hypothesize that Ydj1 transmits growth capacity information to the cell cycle for setting efficient size/ploidy ratios.
G1期细胞周期蛋白Cln3在芽殖酵母中连接细胞生长和增殖过程中起着关键作用。通常认为，在整个G1期都存在的Cln3会被动地在细胞核中积累，直到达到触发细胞周期进入的阈值。我们在此表明，Cln3在G1早期细胞中与内质网（ER）结合。内质网保留需要Cln3与细胞周期蛋白依赖性激酶Cdc28结合，其中一部分Cdc28也与内质网相关联。Cln3含有一个伴侣调节Ji结构域，该结构域可抵消Ydj1，Ydj1是Cln3在G1晚期从内质网释放并进入细胞核所必需的J类伴侣蛋白。最后，Ydj1对Cln3的释放和及时进入细胞周期具有限制作用。由于蛋白质合成和核糖体组装速率会影响伴侣蛋白的可用性，我们推测Ydj1将生长能力信息传递给细胞周期，以设定有效的大小/倍性比。
