Lydiate D J, Ikeda H, Hopwood D A
Mol Gen Genet. 1986 Apr;203(1):79-88. doi: 10.1007/BF00330387.
Streptomyces coelicolor A3(2) contains CCC DNA molecules, 2.6 kb in size, with an average copy number of less than one per ten chromosomes. Southern hybridisation revealed, in addition, two linear, integrated copies (A and B) of this "mini-circle" sequence per chromosome. The two integrated copies have similar (if not identical) ends and are present in the same locations in various S. coelicolor A3(2) derivatives. The mini-circle sequence is absent from S. lividans 66 and S. violaceolatus ISP5438 and from several Streptomyces species less closely related to S. coelicolor A3(2). None of a variety of Streptomyces plasmids tested contained homology to the mini-circle sequence. When a 1.8 kb fragment of the mini-circle lacking the ends of the integrated copies was inserted into KC515 (a derivative of the temperate phage phi C31 which is unable to lysogenise host strains by the natural route because the phage attachment site has been deleted) the resulting phage lysogenized S. coelicolor A3(2) (integrating into the genome of this host by homologous recombination with resident minicircle sequences) but not S. lividans or a variety of other phi C31 hosts. In contrast, a KC515 derivative (KC591) carrying the entire 2.6 kb mini-circle sequence linearized at its single BclI site (and therefore containing the integration site of the free mini-circle) lysogenized not only S. coelicolor A3(2) but also S. lividans 66 and most other strains normally lysogenized by phi C31. The KC591 lysogens of the eight Streptomyces species tested contained a linear, integrated prophage with termini apparently identical to those of the linear mini-circle copies of S. coelicolor.(ABSTRACT TRUNCATED AT 250 WORDS)
天蓝色链霉菌A3(2)含有大小为2.6 kb的共价闭合环状（CCC）DNA分子，平均拷贝数少于每十条染色体一个。此外，Southern杂交显示，每条染色体有两个这种“小环”序列的线性整合拷贝（A和B）。这两个整合拷贝具有相似（如果不是相同）的末端，并且存在于各种天蓝色链霉菌A3(2)衍生物的相同位置。变铅青链霉菌66、紫色链霉菌ISP5438以及与天蓝色链霉菌A3(2)亲缘关系较远的几种链霉菌物种中不存在小环序列。所测试的多种链霉菌质粒均与小环序列无同源性。当将缺失整合拷贝末端的1.8 kb小环片段插入KC515（温和噬菌体phi C31的衍生物，由于噬菌体附着位点已缺失，无法通过自然途径使宿主菌株溶源化）时，所得噬菌体可使天蓝色链霉菌A3(2)溶源化（通过与宿主菌中的小环序列同源重组整合到该宿主的基因组中），但不能使变铅青链霉菌或多种其他phi C31宿主溶源化。相反，携带在其单个BclI位点线性化的完整2.6 kb小环序列（因此包含游离小环的整合位点）的KC515衍生物（KC591）不仅可使天蓝色链霉菌A3(2)溶源化，还可使变铅青链霉菌66以及大多数其他通常被phi C31溶源化的菌株溶源化。所测试的八种链霉菌物种的KC591溶源菌含有一个线性整合原噬菌体，其末端显然与天蓝色链霉菌的线性小环拷贝的末端相同。（摘要截短于250字）
