Fronk J, Tank G A, Langmore J P
Biophysics Research Division, University of Michigan, Ann Arbor 48109-2099.
Nucleic Acids Res. 1990 Sep 11;18(17):5255-63. doi: 10.1093/nar/18.17.5255.
Chromatin organization of the early histone gene repeat was studied at the early embryonic stages of the sea urchin S. purpuratus. Micrococcal nuclease digestion showed a highly irregular packaging of the whole repeat at the period of transcriptional activity, which was progressively replaced by more regular nucleosomal arrays upon developmentally programmed inactivation. No evidence for unique positioning of the nucleosomes was found. Regions upstream of each of the genes were hypersensitive to DNAase I digestion in the active state. These regions contained one (H2A and H2B), or two (H3 and H4) well-defined DNAase I cutting sites, or two poorly-defined sites (H1). They mapped within DNA sequences shown previously to be required for proper expression of the genes. Hypersensitivity continued in the hatching blastula, which have a conventional nucleosomal structure and a much reduced transcriptional activity. Hypersensitivity of these regions during morula and early blastula was not dependent on the torsional strain in chromatin, as it was not influenced by extensive gamma ray-induced nicking of the DNA in nuclei. By late blastula no hypersensitive regions were present.
在紫海胆早期胚胎发育阶段，对早期组蛋白基因重复序列的染色质组织进行了研究。微球菌核酸酶消化显示，在转录活性期，整个重复序列的包装高度不规则，而在发育程序性失活后，逐渐被更规则的核小体阵列所取代。未发现核小体独特定位的证据。每个基因上游区域在活性状态下对DNA酶I消化高度敏感。这些区域包含一个（H2A和H2B）或两个（H3和H4）明确的DNA酶I切割位点，或两个不明确的位点（H1）。它们定位在先前显示对基因正确表达必需的DNA序列内。在孵化囊胚中仍存在高敏感性，孵化囊胚具有传统的核小体结构且转录活性大大降低。在桑椹胚和早期囊胚阶段，这些区域的高敏感性不依赖于染色质中的扭转应变，因为它不受细胞核中广泛的γ射线诱导的DNA切口的影响。到囊胚后期，不再存在高敏感区域。
