Bresnick E H, Tze L
University of Wisconsin Medical School, Department of Pharmacology, 387 Medical Science, 1300 University Avenue, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 1997 Apr 29;94(9):4566-71. doi: 10.1073/pnas.94.9.4566.
The human beta-globin locus control region (LCR) consists of four erythroid-specific DNaseI hypersensitive sites (HSs) at the 5' end of the beta-globin cluster. The LCR functions over a long distance on chromosome 11 to regulate transcription and replication of the beta-globin genes. To determine whether the HSs function independently or as an integrated unit, we analyzed the requirements for long-range transcriptional activation. If the HSs function independently, individual HSs would be expected to have long-range activity. In contrast, if long-range activity requires multiple HSs, individual HSs would have a limited functional distance. HS2, HS3, and a miniLCR containing multiple HSs, were separated from a gamma-globin promoter by fragments of phage lambda DNA. After stable transfection into K562 cells, HS2 had strong enhancer activity, but only when positioned close to the promoter. HS3 also had strong enhancer activity, although it was weaker than HS2 and more sensitive to the spacer DNA. The miniLCR had the strongest enhancer activity and functioned even at a distance of 7.3 kb. A model is proposed in which synergistic interactions between HSs confer long-range activation by creating a stable LCR nucleoprotein structure, which is competent for recruiting chromatin-modifying enzymes. These enzymes would mediate the well-characterized activity of the LCR to modulate chromatin structure.
人类β-珠蛋白基因座控制区（LCR）由β-珠蛋白基因簇5'端的四个红系特异性DNaseI高敏位点（HSs）组成。LCR在11号染色体上远距离发挥作用，调控β-珠蛋白基因的转录和复制。为了确定这些HSs是独立发挥功能还是作为一个整合单元发挥功能，我们分析了远距离转录激活的需求。如果HSs独立发挥功能，那么单个HSs应该具有远距离活性。相反，如果远距离活性需要多个HSs，那么单个HSs的功能距离将是有限的。HS2、HS3以及包含多个HSs的微型LCR，通过噬菌体λ DNA片段与γ-珠蛋白启动子分离。稳定转染到K562细胞后，HS2具有很强的增强子活性，但只有当它靠近启动子时才具有该活性。HS3也具有很强的增强子活性，尽管它比HS2弱，并且对间隔DNA更敏感。微型LCR具有最强的增强子活性，甚至在7.3 kb的距离时仍能发挥作用。我们提出了一个模型，其中HSs之间的协同相互作用通过形成一个稳定的LCR核蛋白结构赋予远距离激活能力，该结构能够募集染色质修饰酶。这些酶将介导LCR已被充分表征的调节染色质结构的活性。
