Litt M D, Hansen R S, Hornstra I K, Gartler S M, Yang T P
Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville, Florida 32610, USA.
J Biol Chem. 1997 Jun 6;272(23):14921-6. doi: 10.1074/jbc.272.23.14921.
During the process of 5-aza-2'-deoxycytidine (5aCdr)-induced reactivation of the X-linked human hypoxanthine phosphoribosyltransferase (HPRT) gene on the inactive X chromosome, acquisition of a nuclease-sensitive chromatin conformation in the 5' region occurs before the appearance of HPRT mRNA. In vivo footprinting experiments reported here show that the 5aCdr-induced change in HPRT chromatin structure precedes the appearance of three footprints in the immediate 5' flanking region that are characteristic of the active HPRT allele. These and other data suggest the following sequence of events that lead to the reactivation of the HPRT gene after 5aCdr treatment: (a) hemi-demethylation of the promoter, (b) an "opening" of chromatin structure detectable as increased nuclease sensitivity, (c) transcription factor binding to the promoter, (d) assembly of the transcription complex, and (e) synthesis of HPRT RNA. This sequence of events supports the view that inactive X-linked genes are silenced by a repressive chromatin structure that prevents the binding of transcriptional activators to the promoter.
在5-氮杂-2'-脱氧胞苷（5aCdr）诱导失活X染色体上的X连锁人类次黄嘌呤磷酸核糖转移酶（HPRT）基因重新激活的过程中，5'区域核酸酶敏感染色质构象的获得先于HPRT mRNA的出现。本文报道的体内足迹实验表明，5aCdr诱导的HPRT染色质结构变化先于紧邻5'侧翼区域出现的三个足迹，这些足迹是活跃HPRT等位基因的特征。这些及其他数据提示了5aCdr处理后导致HPRT基因重新激活的以下事件序列：（a）启动子的半去甲基化，（b）可检测为核酸酶敏感性增加的染色质结构“开放”，（c）转录因子与启动子结合，（d）转录复合物的组装，以及（e）HPRT RNA的合成。这一事件序列支持了以下观点，即失活的X连锁基因被抑制性染色质结构沉默，该结构阻止转录激活因子与启动子结合。
