Bohrmann B, Haider M, Kellenberger E
Department of Microbiology, Biozentrum, University of Basel, Switzerland.
Ultramicroscopy. 1993 Feb;49(1-4):235-51. doi: 10.1016/0304-3991(93)90230-u.
Quantitative STEM with the imaging mode of ratio-contrast was investigated in order to evaluate the local concentration of DNA in situ for different kinds of DNA plasms in terms of intracellular packing densities (p.d.). The ability of ratio imaging to suppress thickness variations provided the basis to use unstained sections from cryofixed and freeze-substituted material. The DNA p.d. within the nucleoid of E. coli was determined to be about 100 mg ml-1. Quantitative data concerning the p.d. of DNA in condensed eukaryotic chromatin assuming equal amounts of DNA and protein were evaluated for the first time: approximately 400 mg ml-1 chromatin which corresponds to 200 mg ml-1 DNA. The p.d. of DNA in chromosomes from the dinoflagellate Amphidinium carterae, a eukaryote devoid of histones and with only small relative amounts of histone-like protein, was also found to be of the order of 200 mg ml-1. The highest p.d. of DNA was measured for the head of the bacteriophage T4 with more than 800 mg ml-1, in fair agreement with previous calculations. The results provide further support for a condensation mode of low protein chromatins that involves a liquid-crystalline organization of the DNA filaments.
为了根据细胞内堆积密度（p.d.）评估不同类型DNA质粒原位DNA的局部浓度，研究了采用比率对比成像模式的定量扫描透射电子显微镜（STEM）。比率成像抑制厚度变化的能力为使用来自冷冻固定和冷冻替代材料的未染色切片提供了基础。大肠杆菌类核内的DNA p.d.测定为约100 mg/ml。首次评估了假设DNA和蛋白质含量相等时浓缩真核染色质中DNA p.d.的定量数据：约400 mg/ml染色质，相当于200 mg/ml DNA。在裸甲藻（一种不含组蛋白且仅含有少量类组蛋白的真核生物）的染色体中，DNA的p.d.也被发现约为200 mg/ml。噬菌体T4头部的DNA p.d.最高，超过800 mg/ml，与先前的计算结果相当吻合。这些结果为低蛋白染色质的凝聚模式提供了进一步支持，该模式涉及DNA细丝的液晶组织。
