Nicholson W L, Setlow P
Department of Biochemistry, University of Connecticut Health Center, Farmington 06032.
J Bacteriol. 1990 Jan;172(1):7-14. doi: 10.1128/jb.172.1.7-14.1990.
Plasmid pUB110, isolated from vegetative cells of Bacillus subtilis, has an average of 34 negative supertwists (tau av = -34). This value falls to -30 early in sporulation, and the plasmid in the mother cell compartment maintains a tau av of -30. However, the plasmid within the developing forespore becomes much more negatively supercoiled, reaching a tau av of -47 in the dormant spore. This increased negative supercoiling in the forespore plasmid takes place in parallel with the synthesis of small, acid-soluble spore proteins, alpha and beta; and the plasmid from spores lacking small, acid-soluble proteins alpha and beta has a tau av of -40. The large increase in negative supercoiling of spore plasmid was also observed with Bacillus megaterium and in B. subtilis containing a plasmid with an origin different from that of pUB110. During spore germination plasmid pUB110 rapidly relaxed back to the tau av value characteristic of vegetative cells. It is possible that the observed changes in forespore plasmid topology are involved in modulating gene expression, DNA photochemistry, or both of these parameters in this compartment.
从枯草芽孢杆菌的营养细胞中分离出的质粒pUB110平均有34个负超螺旋（τav = -34）。在芽孢形成早期，该值降至-30，母细胞区室中的质粒维持τav为-30。然而，发育中的前芽孢内的质粒变得负超螺旋程度更高，在休眠孢子中达到τav为-47。前芽孢质粒中这种负超螺旋增加与小的酸溶性芽孢蛋白α和β的合成同时发生；并且来自缺乏小的酸溶性蛋白α和β的孢子的质粒τav为-40。在巨大芽孢杆菌以及含有与pUB110起源不同的质粒的枯草芽孢杆菌中也观察到了芽孢质粒负超螺旋的大幅增加。在芽孢萌发期间，质粒pUB110迅速松弛回到营养细胞特有的τav值。前芽孢质粒拓扑结构中观察到的变化可能参与调节该区室中的基因表达、DNA光化学或这两个参数。
