Chen C W, Yu T W, Lin Y S, Kieser H M, Hopwood D A
Institute of Genetics, National Yang-Ming Medical College, Shih-Pai, Taipei, Taiwan, Republic of China.
Mol Microbiol. 1993 Mar;7(6):925-32. doi: 10.1111/j.1365-2958.1993.tb01183.x.
The SLP2 plasmid had previously been demonstrated genetically to exist in Streptomyces lividans by its ability to promote conjugation and to elicit 'pocks' on recipient (SLP2-) cultures, but it had not been physically detected. Using pulsed-field gel electrophoresis, a 50 kb linear DNA was isolated from SLP2+ but not SLP2- strains of S. lividans, and from Streptomyces coelicolor and Streptomyces parvulus strains to which SLP2 had been transferred by conjugation or transformation. We conclude that this linear DNA is SLP2. The terminal fragments of SLP2 were cloned. The determined sequences revealed a 44bp imperfect terminal inverted repeat. The terminal 12bp sequence of SLP2 was identical to those of two other Streptomyces linear plasmids, pSLA2 and pSCL, and similar to the terminal sequences of another Streptomyces linear plasmid, SCP1. The termini of SLP2 DNA were resistant to digestion by lambda exonuclease and ExoIII. A truncated (probably crippled) copy of Tn4811 is present on the plasmid. While the SLP2 plasmid exists as a free form in the host, a 15.7 kb sequence corresponding to the segment of SLP2 from Tn4811 to the right terminus is also present (at a copy number similar to the free form) elsewhere in the genome of S. lividans. Furthermore, SLP2 is partially homologous to a newly discovered 650 kb linear plasmid in S. parvulus.
此前通过其促进接合的能力以及在受体（SLP2-）培养物上引发“痘斑”的能力，从遗传学角度证明了SLP2质粒存在于淡紫链霉菌中，但尚未对其进行物理检测。使用脉冲场凝胶电泳，从淡紫链霉菌的SLP2 +菌株而非SLP2-菌株中，以及从通过接合或转化已转入SLP2的天蓝色链霉菌和微小链霉菌菌株中分离出了一条50 kb的线性DNA。我们得出结论，这条线性DNA就是SLP2。克隆了SLP2的末端片段。所确定的序列显示出一个44bp的不完全末端反向重复序列。SLP2的末端12bp序列与另外两个链霉菌线性质粒pSLA2和pSCL的末端序列相同，并且与另一个链霉菌线性质粒SCP1的末端序列相似。SLP2 DNA的末端对λ外切核酸酶和ExoIII的消化具有抗性。该质粒上存在一个截短的（可能有缺陷的）Tn4811拷贝。虽然SLP2质粒在宿主中以游离形式存在，但在淡紫链霉菌基因组的其他位置也存在一个与SLP2从Tn4811到右端的片段相对应的15.7 kb序列（拷贝数与游离形式相似）。此外，SLP2与微小链霉菌中一个新发现的650 kb线性质粒部分同源。
