Blair D G, Clewell D B, Sheratt D J, Helinski D R
Proc Natl Acad Sci U S A. 1971 Jan;68(1):210-4. doi: 10.1073/pnas.68.1.210.
Certain bacterial plasmids can be isolated as unique complexes of supercoiled circular DNA and protein. These complexes are distinguished by the conversion of the supercoiled DNA to the relaxed or open-circular DNA form upon treatment with ionic detergents, proteases, or alkali. This report demonstrates that the open-circular DNA resulting from the pronase-induced relaxation of the complexes of colicinogenic factors E(1) (ColE(1)) and E(2) (ColE(2)) possesses a strand-specific break. In each case this break is found in the heavy strand of the DNA as defined by CsCl centrifugation in the presence of poly(U,G). In addition, the ColE(1) and ColE(2) complexes exhibit certain properties that are plasmid specific. Heat treatment, and to a lesser extent pronase treatment, inactivates the ColE(2) complex, making it insensitive to agents that formerly were capable of inducing relaxation (conversion of the DNA to the open-circular form). In contrast, the ColE(1) complex is not inactivated by these treatments. The potential role of these strand-specific relaxation complexes in DNA replication is discussed.
某些细菌质粒可以作为超螺旋环状DNA与蛋白质的独特复合物被分离出来。这些复合物的特点是，在用离子去污剂、蛋白酶或碱处理后，超螺旋DNA会转变为松弛或开环DNA形式。本报告表明，由蛋白酶K诱导的产大肠杆菌素因子E(1)（ColE(1)）和E(2)（ColE(2)）复合物松弛产生的开环DNA具有链特异性断裂。在每种情况下，这种断裂都出现在DNA的重链上，这是由在聚（U，G）存在下的CsCl离心所定义的。此外，ColE(1)和ColE(2)复合物表现出某些质粒特异性的特性。热处理以及程度较轻的蛋白酶K处理会使ColE(2)复合物失活，使其对以前能够诱导松弛（将DNA转变为开环形式）的试剂不敏感。相比之下，ColE(1)复合物不会因这些处理而失活。本文讨论了这些链特异性松弛复合物在DNA复制中的潜在作用。
