Studies on the structure and rearrangements of the linear chromosome of Streptomyces griseus 2247.

本文从分子水平上研究了灰色链霉菌2247菌株线性染色体的结构及其动态重排，得到以下结果.测定了灰色链霉菌2247染色体末端的核苷酸序列，并与其它链霉菌线性染色体和质粒的核苷酸序列进行了比较。未发现保守的末端序列，但有几个反向重复序列。这些序列可以形成发夹环并在线性DNA的复制中起作用。通过紫外线照射菌株2247制备了许多缺失突变体。突变体染色体的缺失大小与拓扑结构之间的关系表明，染色体左侧靠近afsA基因的某些区域对于线性染色体的维持是必不可少的.对404-23、N2和83三个突变体的环状染色体融合点进行了克隆和测序。推测染色体环化是通过左右缺失端之间的非法重组而发生的，而左右缺失端之间没有任何同源性.只有突变体301-22保持线性染色体。发现其染色体发生了复杂的重排。也就是说，染色体的右臂被左臂取代，另外一个新的片段连接到染色体的两个缺失末端。

The structure of the linear chromosome of Streptomyces griseus strain 2247 and its dynamic rearrangements have been studied on molecular level, and the following results were obtained.1. The nucleotide sequence of the chromosomal end of S.griseus 2247 was determined and compared with those of other Streptomyces linear chromosomes and plasmids. The conserved end sequence was not found there but several inverted repeats were. These sequences may form hairpin loops and function in replication of the linear DNA.2. Many deletion mutants have been prepared by UV-irradiation of strain 2247. The relationship between the deletion size and topology of the mutant chromosomes suggests that some region near the afsA gene on the left side of the chromosome is essential for maintenance of the linear chromosome.3. The fusion junctions of the circularized chromosomes in three mutants, 404-23, N2 and 83, were cloned and sequenced. The chromosomal circularization was deduced to occur by illegitimate recombination between the right and left deletion ends which do not have any homology to each other.4. Only the mutant 301-22 keeps a linear chromosome. Complicated rearrangements were found to have occurred on its chromosome. Namely, the right arm of the chromosome was replaced by the left arm, and additionally a new fragment was attached to both deletion ends of the chromosome.