Bellard M, Oudet P, Germond J E, Chambon P
Eur J Biochem. 1976 Nov 15;70(2):543-53. doi: 10.1111/j.1432-1033.1976.tb11046.x.
Electron microscopic evidence indicates that Simian virus 40 (SV40) minichromosomes extracted from infected cells consist of 20 +/- 2 nucleosomes, each containing 190 -- 200 base pairs of DNA. About 50% of the nucleosomes are not close together, but connected by segments of DNA of irregular lengths which correspond to about 15% of the viral genome, irrespective of the ionic strength. Micrococcal nuclease digestion studies show that there is about 200 base pairs of DNA in the biochemical unit of SV40 chromatin. Therefore, the visible internucleosomal DNA of the SV40 minichromosome does not arise from an unfolding of a fraction of the 190 - 200 base pairs of DNA initially wound in the nucleosome. These results support the chromatin model which proposes that the same DNA length is contained in the nucleosome and the biochemical unit. Results from extensive micrococcal nuclease digestion suggest that an SV40 nucleosome consists of a 'core' containing a DNA segment of about 135 base pairs associated to a DNA fragment more susceptible to nuclease attack. The addition of histone H1 results in a striking condensation of the SV40 minichromosome, which supports the assumption that histone H1 is involved in the folding of chromatin fibers.
电子显微镜证据表明，从受感染细胞中提取的猴病毒40（SV40）微型染色体由20±2个核小体组成，每个核小体包含190 - 200个碱基对的DNA。约50%的核小体并非紧密相连，而是由长度不规则的DNA片段连接，这些片段约占病毒基因组的15%，与离子强度无关。微球菌核酸酶消化研究表明，SV40染色质的生化单位中约有200个碱基对的DNA。因此，SV40微型染色体中可见的核小体间DNA并非源于最初缠绕在核小体中的190 - 200个碱基对DNA的一部分展开。这些结果支持了染色质模型，该模型提出核小体和生化单位中包含相同长度的DNA。广泛的微球菌核酸酶消化结果表明，SV40核小体由一个“核心”组成，该“核心”包含一段约135个碱基对的DNA片段，与一个更易受核酸酶攻击的DNA片段相关。组蛋白H1的添加导致SV40微型染色体显著凝聚，这支持了组蛋白H1参与染色质纤维折叠的假设。
