Zheng Lianxing, Dominski Zbigniew, Yang Xiao-Cui, Elms Phillip, Raska Christy S, Borchers Christoph H, Marzluff William F
Department of Biochemistry and Biophysics. Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Mol Cell Biol. 2003 Mar;23(5):1590-601. doi: 10.1128/MCB.23.5.1590-1601.2003.
The replication-dependent histone mRNAs, the only eukaryotic mRNAs that do not have poly(A) tails, are present only in S-phase cells. Coordinate posttranscriptional regulation of histone mRNAs is mediated by the stem-loop at the 3' end of histone mRNAs. The protein that binds the 3' end of histone mRNA, stem-loop binding protein (SLBP), is required for histone pre-mRNA processing and is involved in multiple aspects of histone mRNA metabolism. SLBP is also regulated during the cell cycle, accumulating as cells enter S phase and being rapidly degraded as cells exit S phase. Mutation of any residues in a TTP sequence (amino acids 60 to 62) or mutation of a consensus cyclin binding site (amino acids 99 to 104) stabilizes SLBP in G2 and mitosis. These two threonines are phosphorylated in late S phase, as determined by mass spectrometry (MS) of purified SLBP from late S-phase cells, triggering SLBP degradation. Cells that express a stable SLBP still degrade histone mRNA at the end of S phase, demonstrating that degradation of SLBP is not required for histone mRNA degradation. Nuclear extracts from G1 and G2 cells are deficient in histone pre-mRNA processing, which is restored by addition of recombinant SLBP, indicating that SLBP is the only cell cycle-regulated factor required for histone pre-mRNA processing.
复制依赖型组蛋白mRNA是唯一没有多聚腺苷酸尾的真核mRNA，仅存在于S期细胞中。组蛋白mRNA的转录后协同调控由组蛋白mRNA 3'端的茎环介导。结合组蛋白mRNA 3'端的蛋白，即茎环结合蛋白（SLBP），是组蛋白前体mRNA加工所必需的，并且参与组蛋白mRNA代谢的多个方面。SLBP在细胞周期中也受到调控，在细胞进入S期时积累，在细胞退出S期时迅速降解。TTP序列（氨基酸60至62）中任何残基的突变或共有细胞周期蛋白结合位点（氨基酸99至104）的突变会使SLBP在G2期和有丝分裂期稳定。如通过对来自S期后期细胞的纯化SLBP进行质谱分析（MS）所确定的，这两个苏氨酸在S期后期被磷酸化，从而触发SLBP降解。表达稳定SLBP的细胞在S期末期仍会降解组蛋白mRNA，这表明组蛋白mRNA降解并不需要SLBP的降解。G1期和G2期细胞的核提取物缺乏组蛋白前体mRNA加工能力，通过添加重组SLBP可恢复该能力，这表明SLBP是组蛋白前体mRNA加工所需的唯一受细胞周期调控的因子。
