Hamid Q A, Ali Z
Department of Biochemistry, Banaras Hindu University, Varanasi, India.
Indian J Biochem Biophys. 1995 Dec;32(6):456-66.
Active chromatin fraction from rat liver nuclei has been isolated under the lower ionic strength conditions, to prevent salt induced rearrangement and exchange of linker histone H1. Salt induced higher order folding in these oligonucleosomes was determined by sedimentation, viscosity, aggregation and circular dichroism studies. Sedimentation studies indicate that upon raising the ionic strength from 25 mM to 65 mM (mainly NaCl), active oligonucleosomes show intrafragmental interaction and formation of soluble oligomers. These oligomers disaggregate into unfolded monomers at 90 mM ionic strength. In contrast, oligonucleosomes from inactive genes show gradual increase in intrafragmental higher order folding without any interfragmental interaction on raising salt concentration. A much higher decrease in viscosity of active oligonucleosomes in comparison to bulk oligonucleosomes also support the above conclusion. However, on raising salt concentration above 100 mM NaCl, both the chromatin fractions are capable of forming insoluble aggregates. Decrease in the molar ellipticities of bulk oligonucleosomes at 273 and 282 nm is observed on raising ionic strength from 25 mM to 65 mM. A different pattern of this decrease is observed in case of active oligonucleosomes, indicating adaptation of a different type of salt induced secondary structure of DNA in these oligonucleosomes. Melting profile of DNA from active and bulk chromatin suggests that the base composition of both the chromatin fractions is same.
已在较低离子强度条件下分离出大鼠肝细胞核的活性染色质组分，以防止盐诱导的连接组蛋白H1重排和交换。通过沉降、粘度、聚集和圆二色性研究确定了这些寡核小体中盐诱导的高级折叠。沉降研究表明，当离子强度从25 mM提高到65 mM（主要是NaCl）时，活性寡核小体显示片段内相互作用并形成可溶性寡聚体。这些寡聚体在90 mM离子强度下解聚为未折叠的单体。相比之下，来自非活性基因的寡核小体在提高盐浓度时，片段内高级折叠逐渐增加，且没有任何片段间相互作用。与整体寡核小体相比，活性寡核小体的粘度下降幅度更大，这也支持了上述结论。然而，当盐浓度提高到100 mM NaCl以上时，两种染色质组分都能够形成不溶性聚集体。当离子强度从25 mM提高到65 mM时，观察到整体寡核小体在273和282 nm处的摩尔椭圆率下降。在活性寡核小体中观察到这种下降的不同模式，表明这些寡核小体中DNA的盐诱导二级结构类型不同。活性染色质和整体染色质的DNA熔解曲线表明，两种染色质组分的碱基组成相同。
