Gottesfeld J M, Bloomer L S
Cell. 1980 Oct;21(3):751-60. doi: 10.1016/0092-8674(80)90438-9.
Mild digestion of Xenopus nuclei with micrococcal nuclease results in the cleavage of oocyte-type 5S RNA genes once every four nucleosomes, or about once per tandem repeating unit of 5S DNA. This specific cleavage pattern is observed with nuclei from somatic cells where oocyte-type 5S genes are never transcribed (blood and liver) and with cultured cell nuclei where these genes are in a DNAase I-sensitive chromatin conformation and low level transcription is observed. Cleavage of protein-free DNA with micrococcal nuclease does not result in a specific digestion pattern. The similarity of the nuclease-generated repeat length and the sequence repeat length of oocyte-type 5S genes suggested a sequence-specific arrangement of nucleosomes on these DNA sequences. Restriction endonuclease analysis indicates that micrococcal nuclease preferentially cleaves in a restricted region within the 5S repeating unit, about 200 bp from the single Hind III site. Using specific end-labeled DNA probes derived from cloned 5S DNA we can recognize at least four possible modes of organization of the nucleosomes on 5S DNA. In each of these phase arrangements, functionally significant regions of the 5S gene (start of transcription, middle control region and transcription termination site) are found in or near nucleosome linkers.
用微球菌核酸酶对非洲爪蟾细胞核进行轻度消化，会导致卵母细胞型5S RNA基因每隔四个核小体被切割一次，即大约每一个5S DNA串联重复单元被切割一次。在从未转录过卵母细胞型5S基因的体细胞（血液和肝脏）的细胞核以及这些基因处于对DNA酶I敏感的染色质构象且观察到低水平转录的培养细胞核中，都能观察到这种特定的切割模式。用微球菌核酸酶切割无蛋白质的DNA不会产生特定的消化模式。核酸酶产生的重复长度与卵母细胞型5S基因的序列重复长度相似，这表明核小体在这些DNA序列上存在序列特异性排列。限制性内切酶分析表明，微球菌核酸酶优先在5S重复单元内的一个受限区域切割，该区域距单个Hind III位点约200 bp。使用源自克隆5S DNA的特异性末端标记DNA探针，我们可以识别出5S DNA上核小体至少四种可能的组织模式。在这些相位排列的每一种中，5S基因的功能重要区域（转录起始、中间控制区域和转录终止位点）都位于核小体连接区或其附近。
