Chen Danyang, Hinkley Craig S, Henry R William, Huang Sui
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611, USA.
Mol Biol Cell. 2002 Jan;13(1):276-84. doi: 10.1091/mbc.01-10-0523.
The recruitment of TATA binding protein (TBP) to gene promoters is a critical rate-limiting step in transcriptional regulation for all three eukaryotic RNA polymerases. However, little is known regarding the dynamics of TBP in live mammalian cells. In this report, we examined the distribution and dynamic behavior of green fluorescence protein (GFP)-tagged TBP in live HeLa cells using fluorescence recovery after photobleaching (FRAP) analyses. We observed that GFP-TBP associates with condensed chromosomes throughout mitosis without any FRAP. These results suggest that TBP stably associates with the condensed chromosomes during mitosis. In addition, endogenous TBP and TBP-associated factors (TAFs), specific for RNA polymerase II and III transcription, cofractionated with mitotic chromatin, suggesting that TBP is retained as a TBP-TAF complex on transcriptionally silent chromatin throughout mitosis. In interphase cells, GFP-TBP distributes throughout the nucleoplasm and shows a FRAP that is 100-fold slower than the general transcription factor GFP-TFIIB. This difference supports the idea that TBP and, most likely, TBP-TAF complexes, remain promoter- bound for multiple rounds of transcription. Altogether, our observations demonstrate that there are cell cycle specific characteristics in the dynamic behavior of TBP. We propose a novel model in which the association of TBP-TAF complexes with chromatin during mitosis marks genes for rapid transcriptional activation as cells emerge from mitosis.
TATA结合蛋白(TBP)被招募至基因启动子是所有三种真核生物RNA聚合酶转录调控中的关键限速步骤。然而,关于TBP在活的哺乳动物细胞中的动态变化知之甚少。在本报告中,我们使用光漂白后荧光恢复(FRAP)分析,检测了绿色荧光蛋白(GFP)标记的TBP在活的HeLa细胞中的分布和动态行为。我们观察到,在整个有丝分裂过程中,GFP-TBP都与凝聚的染色体相关联,且没有任何荧光恢复。这些结果表明,在有丝分裂期间,TBP与凝聚的染色体稳定相关。此外,RNA聚合酶II和III转录特异性的内源性TBP和TBP相关因子(TAFs)与有丝分裂染色质共分离,这表明在整个有丝分裂过程中,TBP作为TBP-TAF复合物保留在转录沉默的染色质上。在间期细胞中,GFP-TBP分布于整个核质,并表现出比一般转录因子GFP-TFIIB慢100倍的荧光恢复。这种差异支持了TBP以及很可能TBP-TAF复合物在多轮转录中仍与启动子结合的观点。总之,我们的观察结果表明,TBP的动态行为存在细胞周期特异性特征。我们提出了一个新模型,即在有丝分裂期间,TBP-TAF复合物与染色质的结合标记了细胞从有丝分裂中出来时快速转录激活的基因。