Hitchins A D
Can J Microbiol. 1978 Oct;24(10):1227-35. doi: 10.1139/m78-197.
The effect of chromosome age on segregation during sporulation was investigated. Vegetative cells of Bacillus megaterium were labeled with [Me-3H]thymine and then were grown at 30 degrees C in nonradioactive medium for various times before being allowed to sporulate. The ratio of the amount of label in sporal DNA to that in sporangial DNA, obtained after minor correction for the sporulation frequency, remained essentially constant as the postlabeling growth period was increased from one to seven generations. The spores were preferentially located at the older poles of sporangia, i.e. the poles formed by divisions occurring prior to those forming the sporangia. Therefore, it seems that old (labeled) chromosomes segregate randomly with respect to both the morphological and genealogical polarities of sporangia. Examination of total cell lysates by dye-buoyant density gradient centrifugation revealed the presence of covalently closed circular DNA from cells grown at 37 degrees C, but none was obtained from cells grown at 30 degrees C. Thus, possible interference by large amounts of extrachromosomal DNA in the determination of the chromosomal segregation pattern is unlikely.
研究了染色体年龄对芽孢形成过程中染色体分离的影响。巨大芽孢杆菌的营养细胞用[甲基-³H]胸腺嘧啶标记，然后在30℃的非放射性培养基中培养不同时间，再使其形成芽孢。在对芽孢形成频率进行微小校正后，芽孢DNA中的标记量与芽孢囊DNA中的标记量之比，在标记后生长期从一代增加到七代时基本保持恒定。芽孢优先位于芽孢囊较老的极，即由在形成芽孢囊之前发生的分裂所形成的极。因此，似乎旧的（标记的）染色体相对于芽孢囊的形态极性和谱系极性都是随机分离的。通过染料浮力密度梯度离心法对总细胞裂解物进行检测，结果显示在37℃生长的细胞中存在共价闭合环状DNA，但在30℃生长的细胞中未检测到。因此，大量染色体外DNA在染色体分离模式测定中产生干扰的可能性不大。
