Barratt M J, Hazzalin C A, Zhelev N, Mahadevan L C
Nuclear Signalling Laboratory, Randall Institute, King's College London, UK.
EMBO J. 1994 Oct 3;13(19):4524-35. doi: 10.1002/j.1460-2075.1994.tb06774.x.
The rapid, transient induction of 80-100 immediate-early (IE) genes upon mitogenic stimulation occurs irrespective of protein synthesis and is mediated by modification of existing proteins. Two mechanisms, not mutually exclusive, involving modification either of sequence-specific transcription factors or of structural chromatin proteins primed by pre-association with responsive effectors are conceivable. Here, we show that upon IE gene induction, the non-histone high-mobility-group protein HMG-14, but not the related protein HMG-17, becomes serine phosphorylated in its basic, amino-terminal region close to where it binds nucleosomal DNA. Phosphorylation, normally transient, occurs independent of transcription and is quantitative and prolonged during superinduction. Brief micrococcal nuclease digestion substantially releases HMG-14 from nuclei in the mononucleosome-bound state. Finally, mononucleosomes prepared from mitogen-stimulated, but not control, cells contain a mitogen-activated kinase that phosphorylates HMG-14 in vitro on the same site(s) as in intact cells. The association of HMG-14 and its mitogen-activated kinase with nuclease-sensitive mononucleosomes has implications for models of mitogen-stimulated IE gene induction.
在有丝分裂原刺激下，80 - 100个立即早期（IE）基因迅速、短暂地被诱导，这一过程与蛋白质合成无关，而是由现有蛋白质的修饰介导的。可以想象有两种并非相互排斥的机制，一种涉及序列特异性转录因子的修饰，另一种涉及与反应性效应物预先结合引发的结构性染色质蛋白的修饰。在此，我们表明，在IE基因诱导时，非组蛋白高迁移率族蛋白HMG - 14，而非相关蛋白HMG - 17，在其靠近结合核小体DNA的碱性氨基末端区域发生丝氨酸磷酸化。磷酸化通常是短暂的，其发生与转录无关，并且在超诱导过程中是定量且持续时间延长的。短暂的微球菌核酸酶消化能使处于单核小体结合状态的HMG - 14从细胞核中大量释放出来。最后，从有丝分裂原刺激的细胞而非对照细胞中制备的单核小体含有一种有丝分裂原激活激酶，该激酶在体外能在与完整细胞相同的位点使HMG - 14磷酸化。HMG - 14及其有丝分裂原激活激酶与核酸酶敏感的单核小体的结合对有丝分裂原刺激的IE基因诱导模型具有重要意义。
