Pelling C, Allen T D
Max Planck Institute für Biologie, Tübingen, Germany.
Chromosome Res. 1993 Nov;1(4):221-37. doi: 10.1007/BF00710128.
The structure of polytene chromosomes has been observed by conventional scanning electron microscopy and also with a high resolution 'in lens' field emission instrument. Surface imaging with secondary electron emission has characterized condensed chromatin and regions known for their RNA synthetic potential (nucleoli, Balbiani rings and puffs). In DNA-rich bands pairing of chromatids appears so perfect that individual chromomeres cannot be visualized as discrete units. In the interbands only chromatid bundles appear as elements, but not individual chromatids. High resolution scanning electron microscopy allows resolution at the nucleosome level. Improved localization of chromosomal structures is demonstrated, as in the case of the proposed separation of the prepupal 'Balbiani ring 1'. Surface images of the RNA synthetic centres of the salivary gland cell are presented. Transcripts of the Balbiani ring template can be observed in the condensed and gradually unfolded state, allowing measurement of unit ribonucleoparticles. The surfaces of puffs have been visualized and are characterized by multiple supercoiled loop structures, which are described according to size, conformation and distribution.
通过传统扫描电子显微镜以及高分辨率的“镜内”场发射仪器对多线染色体的结构进行了观察。利用二次电子发射进行表面成像，已对浓缩染色质以及以其RNA合成潜力而闻名的区域（核仁、巴尔比亚尼环和胀泡）进行了表征。在富含DNA的带中，染色单体的配对看起来非常完美，以至于单个染色粒无法作为离散单元被观察到。在间带中，只有染色单体束作为元件出现，而不是单个染色单体。高分辨率扫描电子显微镜能够在核小体水平实现分辨。如在拟蛹期“巴尔比亚尼环1”的分离情况中所示，染色体结构的定位得到了改善。展示了唾液腺细胞RNA合成中心的表面图像。可以观察到巴尔比亚尼环模板的转录本处于浓缩和逐渐展开的状态，从而能够测量单位核糖核蛋白颗粒。胀泡的表面已被可视化，其特征是具有多个超螺旋环结构，并根据大小、构象和分布进行了描述。
