Phosphorylation of threonine 61 by cyclin A/Cdk1 triggers degradation of stem-loop binding protein at the end of S phase
Phosphorylation of threonine 61 by cyclin A/Cdk1 triggers degradation of stem-loop binding protein at the end of S phase
复制标题
DOI：
10.1128/mcb.01416-07
复制
发表时间：
2008-07-01
影响因子：
5.3
通讯作者：
Marzluff, William F.
中科院分区：
文献类型：
--
作者：
Koseoglu, M. Murat;Graves, Lee M.;Marzluff, William F.
组蛋白基因水平受细胞周期调控，其中一个主要的调控机制是茎环结合蛋白对S期的限制。在S期结束时，SLBP的降解导致组蛋白mRNA生物合成的停止，阻止组蛋白mRNA的积累，直到SLBP在进入下一个S期之前合成。SLBP的降解需要一个SFTTP(58到62)和KRKL(95到98)序列，这是一个可能的周期蛋白结合位点。与谷胱甘肽S转移酶(GST)融合的融合蛋白具有58个氨基酸序列(51~108位氨基酸)，足以模拟S晚期SLBP的降解。以GST-SLBP融合蛋白为底物，我们发现细胞周期蛋白A/CDK1磷酸化Thr61。此外，通过RNA干扰抑制CDK1使SLBP稳定在S期末期。在体外，Thr61的磷酸化是CK2随后对Thr60进行磷酸化所必需的。在S期末，CK2抑制剂也能抑制SLBP的降解。因此，Cyclin A/CDK1对Thr61的磷酸化启动了CK2对Thr60的磷酸化，并负责启动SLBP的降解。我们的结论是，细胞周期蛋白A/CDK1活性在S期末的增加触发了S/G期SLBP的降解(2)。
Histone mRNA levels are cell cycle regulated, and a major regulatory mechanism is restriction of stem-loop binding protein (SLBP) to S phase. Degradation of SLBP at the end of S phase results in cessation of histone mRNA biosynthesis, preventing accumulation of histone mRNA until SLBP is synthesized just before entry into the next S phase. Degradation of SLBP requires an SFTTP (58 to 62) and KRKL (95 to 98) sequence, which is a putative cyclin binding site. A fusion protein with the 58-amino-acid sequence of SLBP (amino acids 51 to 108) fused to glutathione S-transferase (GST) is sufficient to mimic SLBP degradation at late S phase. Using GST-SLBP fusion proteins as a substrate, we show that cyclin A/Cdk1 phosphorylates Thr61. Furthermore, knockdown of Cdk1 by RNA interference stabilizes SLBP at the end of S phase. Phosphorylation of Thr61 is necessary for subsequent phosphorylation of Thr60 by CK2 in vitro. Inhibitors of CK2 also prevent degradation of SLBP at the end of S phase. Thus, phosphorylation of Thr61 by cyclin A/Cdk1 primes phosphorylation of Thr60 by CK2 and is responsible for initiating SLBP degradation. We conclude that the increase in cyclin A/Cdk1 activity at the end of S phase triggers degradation of SLBP at S/G(2).