Townsend D E, Bolton S, Ashdown N, Annear D I, Grubb W B
Aust J Exp Biol Med Sci. 1986 Aug;64 ( Pt 4):367-79. doi: 10.1038/icb.1986.39.
Two staphylococcal plasmids, pWG4 and pWG25, encode production of a diffusible pigment and resistance to erythromycin and spectinomycin. The former was found occurring naturally in a clinical isolate of Staphylococcus aureus and the latter in S. epidermidis. Both plasmids are conjugative, capable of high-frequency, interspecies transfer, only isolated in the open-circular form and identical in molecular weight and pattern of restriction-endonuclease fragments. The only difference between the plasmids is in the expression of resistance, pWG4 encoding inducible and pWG25 constitutive erythromycin resistance. The resistance determinants of both plasmids behave as hitch-hiking transposons in cultural conditions that favour phage-mediated or phage-independent conjugation, always inserting a copy of themselves into the recipient's chromosome, except in S. epidermidis in which the chromosomal insertion site may be absent. The resistance determinants have been cloned and located on a 4 X 7 kbp EcoR1/HindIII restriction fragment which has a restriction map similar to that of the right arm of Tn554 (Murphy and Lofdahl, 1984). The hitch-hiking transposon of plasmid pWG25 has been designated Tn3853.
两种葡萄球菌质粒pWG4和pWG25，编码一种可扩散色素的产生以及对红霉素和壮观霉素的抗性。前者在金黄色葡萄球菌的临床分离株中自然存在，后者在表皮葡萄球菌中存在。这两种质粒都是接合型的，能够进行高频种间转移，仅以开环形式分离，分子量和限制性内切酶片段模式相同。这两种质粒之间的唯一区别在于抗性表达，pWG4编码诱导型红霉素抗性，pWG25编码组成型红霉素抗性。在有利于噬菌体介导或噬菌体非依赖性接合的培养条件下，这两种质粒的抗性决定子表现为搭便车转座子，总是将自身的一个拷贝插入受体染色体中，但在表皮葡萄球菌中可能不存在染色体插入位点。抗性决定子已被克隆，并定位在一个4×7kbp的EcoR1/HindIII限制性片段上，该片段的限制性图谱与Tn554右臂的图谱相似（Murphy和Lofdahl，1984）。质粒pWG25的搭便车转座子已被命名为Tn3853。
