Wang J C
J Cell Sci Suppl. 1984;1:21-9. doi: 10.1242/jcs.1984.supplement_1.2.
In prokaryotic organisms, there is strong evidence that the DNA is underwound or negatively supercoiled. The degree of supercoiling of intracellular DNA is less certain, and various estimates that can be made from existing data place the specific linking difference (superhelical density) of intracellular DNA in prokaryotes around -0.04. The effects of negative supercoiling on DNA structure are illustrated by the flipping of alternating C-G or T-G sequences from right-handed B-helical form to the left-handed Z-helical form. For a plasmid containing a 42 base-pair alternating C-G insert, the B-to-Z transition occurs at a specific linking difference of 0.031 in a dilute aqueous buffer; the same transition occurs at a specific linking difference of -0.041 for a plasmid containing a 42 base-pair alternating T-G insert. The probing of the structure of a particular sequence of intracellular DNA is discussed.
在原核生物中，有充分证据表明DNA处于解旋状态或负超螺旋状态。细胞内DNA的超螺旋程度不太确定，根据现有数据进行的各种估计表明，原核生物细胞内DNA的比连环差（超螺旋密度）约为-0.04。负超螺旋对DNA结构的影响通过交替的C-G或T-G序列从右手B-螺旋形式翻转到左手Z-螺旋形式得到说明。对于含有42个碱基对交替C-G插入片段的质粒，在稀水溶液缓冲液中，B-Z转变发生在比连环差为0.031时；对于含有42个碱基对交替T-G插入片段的质粒，相同的转变发生在比连环差为-0.041时。文中还讨论了对细胞内特定DNA序列结构的探测。
