Birnboim H C
Cell. 1975 Jun;5(2):173-81. doi: 10.1016/0092-8674(75)90025-2.
Very long runs of pyrimidine nucleotides (polypyrimidines), previously detected in DNA from Drosophila melanogaster, have now been localized to a "cryptic" satellite. These polypyrimidines have an average length of 750 nucleotides and account for about 3% of the thymine residues in total DNA. The buoyant density of the DNA component which contains the polypyrimidines was detected by centrifuging native DNA to equilibrium in a CsCl gradient, and then assaying each fraction for its content of polypyrimidines. A peak was detected at adensity of about 1.707 gm/cm-3, distinctly heavier than the main band of DNA (1.702 gm/cm-3). The buoyant density of polypyrimidine-containing molecules was little affected by differences in the molecular weight of the starting DNA in the range 10-5-10-7 daltons (single-stranded). Thus polypyrimidines (and their complementary polypurines) appear to form all or part of a "cryptic" satellite. Polypyrimidines have been isolated and characterized with respect to composition and buoyant density. Direct nucleoside analysis of unlabeled material indicated 34.5% deoxycylidine, 65.5% thymidine. Their banding position in neutral and alkaline CsCl gradients was consistent with a single-stranded DNA polymer of this composition.
此前在黑腹果蝇的DNA中检测到的极长的嘧啶核苷酸链（多嘧啶链），现已定位到一种“隐蔽”卫星DNA上。这些多嘧啶链平均长度为750个核苷酸，约占总DNA中胸腺嘧啶残基的3%。通过在CsCl梯度中对天然DNA进行离心至平衡，然后检测每个组分中多嘧啶链的含量，来测定含有多嘧啶链的DNA组分的浮力密度。在密度约为1.707克/立方厘米处检测到一个峰，明显比DNA的主带（1.702克/立方厘米）重。含多嘧啶链分子的浮力密度受起始DNA分子量在10^-5 - 10^-7道尔顿（单链）范围内差异的影响很小。因此，多嘧啶链（及其互补的多嘌呤链）似乎构成了一种“隐蔽”卫星DNA的全部或部分。已对多嘧啶链进行了分离，并对其组成和浮力密度进行了表征。对未标记物质的直接核苷分析表明，其中34.5%为脱氧胞苷，65.5%为胸苷。它们在中性和碱性CsCl梯度中的条带位置与这种组成的单链DNA聚合物一致。
