Khan S A, Carleton S M, Novick R P
Proc Natl Acad Sci U S A. 1981 Aug;78(8):4902-6. doi: 10.1073/pnas.78.8.4902.
PT181 is a naturally occurring 4.5-kilobase Staphylococcus aureus plasmid encoding resistance to tetracycline. The plasmid has a copy number of about 20 per cell; a mutant, cop-608, that has a copy number of 800-1000 has been isolated. A cell-free extract has been developed that carries out complete replication of this plasmid. Extracts made from a strain containing the mutant have much greater replication activity than do extracts of strains containing pT181. In an extract from which endogenous DNA has been removed, DNA synthesis is dependent upon the addition of exogenous plasmid DNA. The replication system is specific for pT181 and related plasmids but it is inactive with other S. aureus plasmids. Furthermore, pT181 DNA does not replicate in extracts made from plasmid-negative strains or strains containing other plasmids. The results suggest that a specific plasmid-encoded substance is required for the replication of pT181 DNA.
PT181是一种天然存在的4.5千碱基的金黄色葡萄球菌质粒，编码对四环素的抗性。该质粒的拷贝数约为每个细胞20个；已分离出一个拷贝数为800 - 1000的突变体cop - 608。已经开发出一种无细胞提取物，它能实现该质粒的完全复制。从含有突变体的菌株中制备的提取物比含有pT181的菌株提取物具有更高的复制活性。在去除了内源DNA的提取物中，DNA合成依赖于添加外源质粒DNA。该复制系统对pT181和相关质粒具有特异性，但对其他金黄色葡萄球菌质粒无活性。此外，pT181 DNA在由质粒阴性菌株或含有其他质粒的菌株制备的提取物中不复制。结果表明，pT181 DNA的复制需要一种特定的质粒编码物质。
