Ryan J L, Morowitz H J
Proc Natl Acad Sci U S A. 1969 Aug;63(4):1282-9. doi: 10.1073/pnas.63.4.1282.
Precise optical melting profiles of purified DNA from Mycoplasma sp. (Kid) show a secondary hyperchromic rise, corresponding to 1.4 per cent of the total DNA, occurring at 88 degrees C, while the bulk of the DNA melts at 79.5 degrees C, indicating an average base composition of 24.9 per cent guanine-cytosine (G-C). A method is presented, using sonication followed by hydroxyapatite column chromatography, for the partial purification of regions of a genome which contain significantly higher G-C than the average value for the genome. The procedure does not involve denaturation and renaturation of the high G-C material so that purified DNA is in its native, double-stranded state and has a normal melting profile. When applied to Mycoplasma sp. (Kid), the method yielded a fraction of native DNA enriched 40 times with respect to those regions coding for rRNA and tRNA. This enriched DNA has a saturation hybridization value of 15.9 per cent with Kid rRNA plus tRNA. The saturation hybridization values of the bulk DNA with rRNA and tRNA are 0.26 per cent and 0.16 per cent, respectively. Based on a genome size of 6.84 x 10(8), obtained by electron microscopy, this indicates that Mycoplasma sp. (Kid) contains only enough ribosomal DNA to code for one set of 23S plus 16S rRNA and only enough DNA complementary to tRNA to code for 44 different tRNA molecules.
来自支原体属（Kid株）的纯化DNA的精确光学解链图谱显示，在88℃时出现了二次增色上升，相当于总DNA的1.4%，而大部分DNA在79.5℃时解链，表明鸟嘌呤-胞嘧啶（G-C）的平均碱基组成为24.9%。本文介绍了一种方法，通过超声处理后进行羟基磷灰石柱色谱法，对基因组中G-C含量显著高于基因组平均值的区域进行部分纯化。该方法不涉及高G-C含量物质的变性和复性，因此纯化后的DNA处于天然双链状态，具有正常的解链图谱。当应用于支原体属（Kid株）时，该方法得到了相对于编码rRNA和tRNA的区域富集40倍的天然DNA片段。这种富集的DNA与Kid rRNA加tRNA的饱和杂交值为15.9%。总体DNA与rRNA和tRNA的饱和杂交值分别为0.26%和0.16%。基于电子显微镜获得的6.84×10⁸的基因组大小，这表明支原体属（Kid株）仅含有足够编码一套23S加16S rRNA的核糖体DNA，以及仅含有足够与tRNA互补以编码44种不同tRNA分子的DNA。
