Kimura T, Mills F C, Allan J, Gould H
Nature. 1983;306(5944):709-12. doi: 10.1038/306709a0.
Globin gene expression, which occurs exclusively in the erythroid cell lineage, is controlled at the level of transcription. It is thus of some considerable interest to compare the chromatin structure of this gene with that of inactive genes in erythroid cell nuclei and to compare the chromatin structure of the globin gene in its active and inactive states in nuclei of different cell types. Other workers have observed that globin genes in erythroid cell nuclei exhibit the enhanced overall sensitivity to nucleases and the hypersensitive site in the 5'-flanking sequence typical of many active genes. The nature of the structural changes giving rise to nuclease sensitivity are however obscure. We have investigated the local higher order structure of chromatin in the region of unique genes in chicken by sucrose gradient sedimentation of chromatin restriction fragments. We find that ovalbumin and alpha 2-collagen gene fragments in erythrocyte chromatin and an adult beta-globin gene fragment in spleen chromatin sediment with bulk chromatin fragments of the same DNA size, whereas the beta-globin gene fragment in erythrocyte chromatin sediments more slowly than bulk fragments of equivalent size. The simplest interpretation of the results is that the solenoid structure in the region of the globin gene is selectively and permanently unfolded on gene activation.
珠蛋白基因表达仅发生在红细胞系中，且在转录水平受到调控。因此，将该基因的染色质结构与红细胞细胞核中无活性基因的染色质结构进行比较，并比较不同细胞类型细胞核中处于活性和非活性状态的珠蛋白基因的染色质结构，具有相当大的研究意义。其他研究人员观察到，红细胞细胞核中的珠蛋白基因对核酸酶的总体敏感性增强，且在5'-侧翼序列中存在超敏位点，这是许多活性基因的典型特征。然而，导致核酸酶敏感性的结构变化的本质尚不清楚。我们通过对染色质限制性片段进行蔗糖梯度沉降，研究了鸡中独特基因区域的染色质局部高级结构。我们发现，红细胞染色质中的卵清蛋白和α2-胶原蛋白基因片段以及脾染色质中的成年β-珠蛋白基因片段与相同DNA大小的大量染色质片段一起沉降，而红细胞染色质中的β-珠蛋白基因片段沉降速度比同等大小的大量片段慢。对结果最简单的解释是，珠蛋白基因区域的螺线管结构在基因激活时被选择性地、永久性地展开。
