Kitzis A, Leibovitch S A, Leibovitch M P, Tichonicky L, Harel J, Kruh J
Biochim Biophys Acta. 1982 Apr 26;697(1):60-70. doi: 10.1016/0167-4781(82)90045-8.
It was shown with the use of specific probes that mild micrococcal nuclease digestion released from chromatin actively-transcribed genes as small nucleosome oligomers. In the present work we demonstrate that most if not all of the active genes are accessible to the nuclease. It was found that the short released fragments are greatly enriched in transcribed DNA sequences, the most enriched being the dimers of nucleosomes since 35% of their DNA could be hybridized to cytoplasmic RNA. The results of cDNA-DNA hybridizations indicate that the monomers and dimers of nucleosomes contain most of the DNA sequences which encode poly(A+) RNAs, however larger released fragments include some transcribed sequences, while the nuclease resistant chromatin is considerably impoverished in coding sites. These evidences are the finding that about 25% of the DNA from the dimers of nucleosomes are exclusively located in this class of fragments, tend to prove that the active chromatin regions are attacked in a non-random way by micrococcal nuclease. We have previously isolated, without using exogenous nuclease, an actively transcribed genomic fraction amounting to 1.5-2% of the total nuclear DNA, formed of single-stranded DNA. In the present study we show that all or nearly all the single-stranded DNA sequences could be reassociated with the DNA fragments present in the released monomers and dimers of nucleosomes. Our observations confirmed our previous finding that the greatest part of single-stranded DNA selectively originates from the coding strand of genomic DNA.
使用特异性探针显示，温和的微球菌核酸酶消化从染色质中释放出作为小核小体寡聚体的活跃转录基因。在本研究中，我们证明大多数（如果不是全部）活跃基因对核酸酶是可及的。发现释放出的短片段在转录的DNA序列中高度富集，最富集的是核小体二聚体，因为其35%的DNA可与细胞质RNA杂交。cDNA-DNA杂交结果表明，核小体的单体和二聚体包含了大多数编码聚（A+）RNA的DNA序列，然而较大的释放片段包含一些转录序列，而对核酸酶有抗性的染色质在编码位点上则相当贫乏。这些证据以及发现核小体二聚体中约25%的DNA仅存在于此类片段中，倾向于证明活跃染色质区域受到微球菌核酸酶的非随机攻击。我们之前在不使用外源性核酸酶的情况下分离出了一个活跃转录的基因组组分，其占总核DNA的1.5 - 2%，由单链DNA组成。在本研究中我们表明，所有或几乎所有的单链DNA序列都可以与释放出的核小体单体和二聚体中的DNA片段重新结合。我们的观察结果证实了我们之前的发现，即单链DNA的最大部分选择性地起源于基因组DNA的编码链。
