应用原子力显微镜对玉米染色质纤丝及染色体骨架的研究(英文)

The Atomic Force Microscopic Examination of Chromatin Fibril and Chromosome Scaffold in Maize

应用原子力显微镜对经化学方法预处理的玉米染色体超微结构进行了研究。原子力显微镜观察的结果揭示,经30%醋酸处理的玉米染色体表面呈现出不均一的颗粒状结构。当缩小扫描范围后,在染色体表面发现直径分别为30和100 nm的两种染色质纤丝。100 nm的染色质纤丝由30 nm染色质纤丝螺旋缠绕而成。在经25%胰酶处理的玉米染色体上发现了两种类似的螺旋状染色质纤丝结构,其直径分别为30和100～150 nm。较细的染色质纤丝螺旋缠绕成较粗的纤丝,进而构成整个染色体。经低离子浓度溶液抽提,用原子力显微镜观察到了玉米染色体的染色体骨架结构。这种染色体骨架呈不规则的纤维网状,这些网状纤维在染色体中部显得较为紧密,在染色体的边缘则显得较松散。这一结果暗示染色体是由不同级别的染色质纤丝螺旋缠绕构成,为染色体的多级螺旋结构假说提供了新的证据。同时发现染色体骨架并不是呈轴样的结构存在,而是保留了染色体的基本形态,这种骨架形状也许是由分散在染色体中的染色体骨架蛋白在低离子浓度溶液抽提的过程中凝缩形成的。

Atomic force microscope（AFM）was employed to investigate the surface structure of maize chromosomefollowing some chemical treatments.After the contaminants covering chromosome removed by 30%acetic acid,twolevels of chromatin fibers on the surface of chromosome were observed.It seemed that the 30 nm fibers were coiled intothick fibers whose diameter was about 100 nm.Two kinds of analogical fibrous structures（diameters were about 30 nmand 100~150 nm）could be observed on the chromosome after 0.25%trypsin treatment.The thick fiber was twisted bythe thin fiber and aggregated into the entire chromosome.After dextran sulphate/heparin solution treatment,fibrouschromosome scaffolds（CS）were observed,it showed an irregular fibrous network structure on the chromosome.Theseresults indicated that the chromosome may be formed by different levels of chromatin,and the CS may not be anintegrated structure,but can be formed by some discrete residual protein cross-links that supported the integrity of thechromosome structure.