短DNA片段缩合结构的比较研究

A COMPARATIVE STUDY ON CONDENSED STRUCTURES OF SHORT DNA FRAGMENTS

本文利用透射式电镜对四种短DNA片段(500、1100、1500、2700 bP)的缩合结构进行了比较研究得出很有意义的结果。定量研究证实短至500 bP的DNA分子仍可形成复曲面,且分子量相差5倍多的DNA片段缩合形成的复曲面尺度大小一致。复曲面外径为400A左右。从而进一步证实作者与Arscott及Bloomfield关于复曲面尺度独立于DNA分子量,及短DNA片段的缩合是多分子缩合的结论。此外,观测到缩合中间结构的尺度依DNA分子量大小不同而变化,同时分子量愈小的DNA片段产生另一种缩合结构—棒体的几率愈大。

The condensed structures produced from 500, 1100, 1500 and 2700 base pair fragments of plasmid PLC13 DNA was investigated in detail by Electron Microscopy. Very short DNA fragments down to 500 bp could still form toroids by condensation; and no significant difference in dimensions of toroids was found between the above four fragments though there is a difference in molecular weight for more than five folds between the longest and shortest DNA fragments. Theouter radii of toroids are around .100 A. The facts give further evidence that the dimension of toroids are independent of DNA molecular weight; The condensed particles are multimericj and only multimolecular condensation occurs in short DNA fragments.Meanwhile, differences in dimensions of intermediate structures formed by different length of DNA fragments were observed; and much more rods (another condensed structure) were formed when condensation took place in the shortest DNA fragments.