Van't Hof J, Bjerknes C A
Mol Cell Biol. 1982 Apr;2(4):339-45. doi: 10.1128/mcb.2.4.339-345.1982.
Velocity sedimentation in an alkaline sucrose gradient of newly replicated chromosomal DNA revealed the presence of extrachromosomal DNA that was not replicated by differentiating cells in the elongation zone. The extrachromosomal DNA had a number average molecular weight of 12 X 10(6) to 15 X 10(6) and a weight average molecular weight of 25 X 10(6), corresponding to about 26 X 10(6) and 50 X 10(6) daltons, respectively, of double-stranded DNA. The molecules were stable, lasting at least 72 h after being formed. Concurrent measurements by velocity sedimentation, autoradiography, and cytophotometry of isolated nuclei indicated that the extrachromosomal molecules were associated with root-tip cells that stopped dividing and differentiated from G2 phase but not with those that stopped dividing and differentiated from G1 phase.
在碱性蔗糖梯度中对新复制的染色体DNA进行速度沉降分析，结果显示存在一种染色体外DNA，该DNA在伸长区的分化细胞中未被复制。这种染色体外DNA的数均分子量为12×10⁶至15×10⁶，重均分子量为25×10⁶，分别对应双链DNA约26×10⁶和50×10⁶道尔顿。这些分子很稳定，形成后至少能持续72小时。通过对分离细胞核进行速度沉降、放射自显影和细胞光度测定的同步测量表明，染色体外分子与从G2期停止分裂并分化的根尖细胞相关，而与从G1期停止分裂并分化的细胞无关。
