Bazett-Jones D P, Hendzel M J
Department of Cell Biology and Anatomy, University of Calgary, 3330 Hospital Drive, Calgary, Alberta, T2N 4N1, Canada.
Methods. 1999 Feb;17(2):188-200. doi: 10.1006/meth.1998.0729.
The analytical electron microscope technique called electron spectroscopic imaging (ESI) has a number of applications in the study of DNA:protein complexes. The method offers an intermediate level of spatial resolution for in vitro structural studies of complexes that may be too large or heterogeneous to study by crystallography or magnetic resonance spectroscopy. An advantage of ESI is that the distribution of nucleic acids can be resolved in a nucleoprotein complex by mapping the element phosphorus, present at high levels in nucleic acid compared to protein. Measurements of phosphorus content together with mass determination allows estimates to be made of stoichiometric relationships of protein and nucleic acids in these complexes. ESI is also suited to in situ studies of nuclear structure. Mass-sensitive images combined with nitrogen and phosphorus maps can be used to distinguish nucleic acid components from nuclear structures that are predominantly protein based. Interactions between chromatin on the periphery of interchromatin granule clusters (IGC) with the protein substructure that connects the exterior of the IGC to its core can be studied with this technique. The method also avoids the use of heavy atom stains, agents required in conventional electron microscopy, that preclude the distinguishing of structures on the basis of their biochemical composition. The principles of ESI and technical aspects of the method are discussed.
被称为电子光谱成像（ESI）的分析电子显微镜技术在DNA：蛋白质复合物的研究中有许多应用。该方法为体外复合物的结构研究提供了中等水平的空间分辨率，这些复合物可能太大或太不均匀而无法通过晶体学或磁共振光谱进行研究。ESI的一个优点是，通过绘制磷元素（与蛋白质相比，核酸中磷的含量很高），可以在核蛋白复合物中分辨出核酸的分布。磷含量的测量与质量测定一起，可以估算这些复合物中蛋白质和核酸的化学计量关系。ESI也适用于核结构的原位研究。结合氮和磷图谱的质量敏感图像可用于区分核酸成分与主要基于蛋白质的核结构。利用该技术可以研究染色质间颗粒簇（IGC）外围的染色质与连接IGC外部与其核心的蛋白质亚结构之间的相互作用。该方法还避免了使用传统电子显微镜所需的重原子染色剂，这些染色剂妨碍了根据生物化学成分区分结构。本文讨论了ESI的原理和该方法的技术方面。
