Mirkin S M, Zaitsev E N, Panyutin I G, Lyamichev V I
Mol Gen Genet. 1984;196(3):508-12. doi: 10.1007/BF00436200.
This study deals with the effects of a temperature-sensitive (ts) mutation at the gene encoding the DNA gyrase B subunit (gyrBts) and a deletion of the top gene encoding the omega protein upon the superhelical density of the pAO3 plasmid in E. coli cells. The alteration of the DNA gyrase B subunit is shown to lead to a partial relaxation of DNA. On the other hand, the lack of omega protein due to the top gene deletion leads to an abnormally high degree of DNA supercoiling. In a double gyrBts delta top mutant the DNA supercoiling is greater than native at the permissive temperature, while under nonpermissive conditions a partial relaxation is observed. However, the pattern of DNA relaxation in the latter case is quite different from that in a single gyrBts mutant. The conclusion is that the native supercoiling of DNA in the cell is maintained through the counter-activities of DNA gyrase and the omega protein.
本研究探讨了编码DNA回旋酶B亚基的基因（gyrBts）上的温度敏感（ts）突变以及编码ω蛋白的top基因缺失对大肠杆菌细胞中pAO3质粒超螺旋密度的影响。结果表明，DNA回旋酶B亚基的改变会导致DNA部分松弛。另一方面，由于top基因缺失导致的ω蛋白缺乏会导致DNA超螺旋程度异常高。在双gyrBts delta top突变体中，在允许温度下DNA超螺旋大于天然状态，而在非允许条件下观察到部分松弛。然而，后一种情况下的DNA松弛模式与单gyrBts突变体中的模式有很大不同。结论是，细胞中DNA原本的超螺旋状态是通过DNA回旋酶和ω蛋白的相反作用来维持的。
