Lin Y S, Chen C W
Institute of Biochemistry, National Yang-Ming University, Shih-Pai, Taipei, Taiwan.
Mol Microbiol. 1997 Nov;26(4):709-19. doi: 10.1046/j.1365-2958.1997.5991975.x.
The chromosomes of Streptomyces species are linear molecules, containing long terminal inverted repeats and covalently bound terminal proteins. These chromosomes undergo spontaneous deletions of the terminal sequences at high frequencies and become circularized in several cases examined. Artificial circularization of the Streptomyces lividans chromosome was also achieved by targeted recombination in vivo, in which the terminal inverted repeats of the chromosome were connected by a kanamycin resistance gene (aphII). Under kanamycin selection, the circularized chromosomes harboured tandem amplifications of a 20.2 kb sequence that included the aphII gene flanked by direct repeats and deletions nearby. On release from kanamycin selection, the aphII amplifications and the neighbouring sequences were deleted from the chromosomes, rendering all the cultures kanamycin sensitive. The chloramphenicol resistance gene, which was prone to deletion in wild-type S. lividans, became much more stable in the kanamycin-sensitive derivatives. These results indicate that the telomeres and/or certain terminal sequences may be involved in the structural instability of Streptomyces chromosomes.
链霉菌属物种的染色体是线性分子，含有长末端反向重复序列和共价结合的末端蛋白。这些染色体在高频率下会自发缺失末端序列，并且在一些检测的案例中会环化。通过体内靶向重组也实现了变铅青链霉菌染色体的人工环化，其中染色体的末端反向重复序列通过卡那霉素抗性基因（aphII）连接。在卡那霉素选择下，环化的染色体含有一个20.2 kb序列的串联扩增，该序列包括两侧有同向重复序列且附近有缺失的aphII基因。从卡那霉素选择中释放后，aphII扩增片段和相邻序列从染色体上删除，使得所有培养物对卡那霉素敏感。在野生型变铅青链霉菌中容易缺失的氯霉素抗性基因，在对卡那霉素敏感的衍生物中变得更加稳定。这些结果表明，端粒和/或某些末端序列可能与链霉菌染色体的结构不稳定性有关。
