Stanisich V A, Bennett P M, Oritz J M
Mol Gen Genet. 1976 Feb 2;143(3):333-7. doi: 10.1007/BF00269412.
The molecular properties of the P-group plasmids R26, R527 and R18-18- (a carbenicillin-sensitive derivative of R18) have been compared with those of RP1. R18-18 and RPI have a MW about 38 X 10(6) daltons, and R26 and R527 of 52 X 10(6) daltons (determined from contour lengths). All three plasmids have a bouyant density similar to that of RPI (1.719 g/cm3, 60% GN. From their molecular and phenotypic similarities, these plasmids probably represent two pairs of identical or closely similar elements. Resistant bacteria are not recovered following F116L-mediated transduction of R26 (or R527), and this correlates with the plasmids' larger size (phage genome=40 X 10(6) daltons). Fragments of R26 are, however, transduced and their resistance determinants may be "rescued" by recombination if the recipient harbours R1818. Such events are accompanied by an increase in the size of the recipient plasmid from 38 X 10(6) to 52 X 10(6) daltons following inheritance of the resistance determinants Sm Su Gm Hg, but not Cb. Thus, Sm Su Gm Hg are encoded in a DNA segment of MW about 14 X 10(6) daltons which apparently has no homologous region on R18-18. Since a piece of DNA of this MW also corresponds to the difference in size between R26 and R18-18, it is possible that the former is derived from an RPI-like element which has acquired these additional resistance determinants.
已将P群质粒R26、R527和R18 - 18（R18的羧苄青霉素敏感衍生物）的分子特性与RP1的分子特性进行了比较。R18 - 18和RP1的分子量约为38×10⁶道尔顿，R26和R527的分子量为52×10⁶道尔顿（由轮廓长度测定）。所有这三种质粒的浮力密度与RP1的相似（1.719 g/cm³，60%甘油）。从它们的分子和表型相似性来看，这些质粒可能代表两对相同或非常相似的元件。在F116L介导的R26（或R527）转导后未回收抗性细菌，这与质粒较大的尺寸相关（噬菌体基因组 = 40×10⁶道尔顿）。然而，R26的片段可被转导，如果受体含有R1818，其抗性决定簇可通过重组“拯救”。在继承抗性决定簇Sm、Su、Gm、Hg（但不是Cb）后，这些事件伴随着受体质粒大小从38×10⁶道尔顿增加到52×10⁶道尔顿。因此，Sm、Su、Gm、Hg由分子量约为14×10⁶道尔顿的DNA片段编码，该片段在R18 - 18上显然没有同源区域。由于这个分子量的一段DNA也对应于R26和R18 - 18之间的大小差异，所以前者可能源自获得了这些额外抗性决定簇的类似RP1的元件。
