McGrath R A, Williams R W
Biophys J. 1967 May;7(3):309-17. doi: 10.1016/S0006-3495(67)86590-1.
The molecular weight of single-stranded DNA from the slime mold Physarum polycephalum has been determined by alkaline gradient centrifugation. The average molecular weight during DNA synthesis ( approximately 1.5 x 10(7) D) is less than that observed in nonsynthetic periods ( approximately 4 x 10(7) D). On the basis of a chromosome number of 50 per nucleus and a DNA content of 1 mumug per nucleus, we are led to conclude that at pH 12 each chromosome dissociates into 300 (single-stranded) pieces of DNA. We have also compared the sedimentation profiles of single-stranded DNA from Escherichia coli, PPLO, and T2 bacteriophage. These data support the conjecture that each bacterial chromosome can be dissociated into 10 or 12 single-stranded pieces of DNA. Dissociation of DNA into multiple pieces under our experimental conditions is best interpreted in terms of interruptions in the continuity of the DNA either by naturally occurring gaps or at alkali-labile bonds.
通过碱性梯度离心法测定了多头绒泡菌单链DNA的分子量。DNA合成期间的平均分子量（约1.5×10⁷道尔顿）小于非合成期观察到的分子量（约4×10⁷道尔顿）。基于每个细胞核有50条染色体且每个细胞核的DNA含量为1微克，我们得出结论：在pH 12时，每条染色体解离成300个（单链）DNA片段。我们还比较了大肠杆菌、支原体和T2噬菌体单链DNA的沉降图谱。这些数据支持了这样的推测：每个细菌染色体可解离成10或12个单链DNA片段。在我们的实验条件下，DNA解离成多个片段，最好根据DNA连续性的中断来解释，这种中断要么是由天然存在的缺口引起，要么是在碱不稳定键处引起。
