Neimark H C, Lange C S
Department of Microbiology and Immunology, State University of New York, Brooklyn 11203.
Nucleic Acids Res. 1990 Sep 25;18(18):5443-8. doi: 10.1093/nar/18.18.5443.
Full-size linear chromosomes were prepared from mycoplasmas by using gamma-irradiation to introduce one (on average) double-strand break in their circular chromosomes. Chromosome sizes were estimated by pulsed-field gel electrophoresis (PFGE) from the mobilities of these full-length molecules relative to DNA size references. Sizes estimated for Ureaplasma urealyticum T960 and 16 Mycoplasma species ranged from 684 kbp (M. hominis) to 1315 kbp (M. iowae). Using this sample, we found no correlation between the mobility of the full-size linear chromosomes and their G + C content. Sizes for A. laidlawii and A. hippikon were within the range expected from renaturation kinetics. PFGE size estimates are in good agreement with sizes determined by other methods, including electron microscopy, an ordered clone library, and summation of restriction fragments. Our estimates also agree with those from renaturation kinetics for both the largest and some of the smallest chromosomes, but in the intermediate size range, renaturation kinetics consistently provides lower values than PFGE or electron microscopy. Our PFGE estimates show that mycoplasma chromosomes span a continual range of sizes, with several intermediate values falling between the previously recognized large and small chromosome size clusters.
通过使用γ射线辐照在支原体的环状染色体中平均引入一个双链断裂，从而制备出全长线性染色体。通过脉冲场凝胶电泳（PFGE），根据这些全长分子相对于DNA大小参照的迁移率来估计染色体大小。对解脲脲原体T960和16种支原体的大小估计范围为684千碱基对（人型支原体）至1315千碱基对（伊氏支原体）。利用该样本，我们发现全长线性染色体的迁移率与其G + C含量之间没有相关性。莱氏无胆甾原体和马无胆甾原体的大小在复性动力学预期的范围内。PFGE大小估计值与通过其他方法确定的大小高度一致，这些方法包括电子显微镜、有序克隆文库以及限制性片段的总和。我们的估计值在最大和一些最小染色体的大小方面也与复性动力学的估计值一致，但在中等大小范围内，复性动力学始终提供比PFGE或电子显微镜更低的值。我们的PFGE估计表明，支原体染色体大小跨度连续，有几个中间值落在先前公认的大、小染色体大小簇之间。
