Rush M G, Gordon C N, Novick R P, Warner R C
Proc Natl Acad Sci U S A. 1969 Aug;63(4):1304-10. doi: 10.1073/pnas.63.4.1304.
A penicillinase plasmid from Staphylococcus aureus and three of its derivatives, all previously identified as extrachromosomal genetic elements, have been isolated in high yield as circular duplex DNA molecules. The wild-type plasmid was found by contour-length measurements of electron micrographs to have a molecular weight of 18.6 x 10(6) daltons. Two plasmids with deletions encompassing six and eight of the eleven known plasmid cistrons had molecular weights of 16.4 x 10(6) and 15.3 x 10(6) daltons, respectively. This information was used to establish approximate physical distances for the genetic map. A high-frequency transducing element also derived from the plasmid had a molecular weight of approximately 24 x 10(6) daltons. Although each plasmid preparation appeared homogeneous by ultracentrifugal analysis, electron micrographs always revealed the presence of a low percentage of complex oligomeric forms, particularly circular and catenated dimers.
从金黄色葡萄球菌中分离出一种青霉素酶质粒及其三种衍生物，所有这些之前都被鉴定为染色体外遗传元件，它们以环状双链DNA分子的形式被高产分离出来。通过电子显微镜照片的轮廓长度测量发现，野生型质粒的分子量为18.6×10⁶道尔顿。两种缺失了已知的11个质粒顺反子中的6个和8个的质粒，分子量分别为16.4×10⁶和15.3×10⁶道尔顿。这些信息被用于确定遗传图谱的大致物理距离。一个同样源自该质粒的高频转导元件的分子量约为24×10⁶道尔顿。尽管通过超速离心分析每种质粒制剂看起来都是均一的，但电子显微镜照片总是显示存在低比例的复杂寡聚形式，特别是环状和连环二聚体。
