Verdin E, Paras P, Van Lint C
Laboratory of Viral and Molecular Pathogenesis, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, MD 20892.
EMBO J. 1993 Aug;12(8):3249-59. doi: 10.1002/j.1460-2075.1993.tb05994.x.
Chromatin organization of eukaryotic promoters is increasingly recognized as an important factor in the regulation of transcription in vivo. To determine the role of chromatin in HIV-1 expression, we have examined the nucleosome organization of the promoter of HIV-1 under low and high transcription rates. Independently of the cell line examined, nucleosomes are precisely positioned in the viral 5' long terminal repeat (5' LTR) and define two large nucleosome-free regions encompassing nt 200-450 and 610-720. A nucleosome positioned between these two regions, immediately after the transcription initiation site (nuc-1), is disrupted following TPA or TNF-alpha treatment. The disruption of nuc-1 from DNA is independent of DNA replication since it is completed in 20 min and independent of transcription as it is alpha-amanitin insensitive. A model is proposed in which nuc-1 plays an organizing role in the HIV-1 promoter to bring in close proximity factors bound to DNA in the two nucleosome-free regions, upstream and downstream of the site of transcription initiation. These results define chromatin as an integral component of the HIV-1 transcriptional regulatory machinery and identify a chromatin transition associated with activation of viral gene expression.
真核生物启动子的染色质组织越来越被认为是体内转录调控的一个重要因素。为了确定染色质在HIV-1表达中的作用，我们研究了HIV-1启动子在低转录率和高转录率下的核小体组织。无论所检测的细胞系如何，核小体都精确地定位在病毒5'长末端重复序列（5'LTR）中，并界定了两个大的无核小体区域，分别包含核苷酸200 - 450和610 - 720。位于这两个区域之间、转录起始位点（nuc-1）之后的一个核小体，在TPA或TNF-α处理后会被破坏。nuc-1从DNA上的解离与DNA复制无关，因为它在20分钟内即可完成，并且与转录无关，因为它对α-鹅膏蕈碱不敏感。我们提出了一个模型，其中nuc-1在HIV-1启动子中发挥组织作用，使结合在转录起始位点上游和下游两个无核小体区域中DNA上的因子紧密靠近。这些结果将染色质定义为HIV-1转录调控机制的一个组成部分，并确定了与病毒基因表达激活相关的染色质转变。
