Moore G P, Scheller R H, Davidson E H, Britten R J
Cell. 1978 Oct;15(2):649-60. doi: 10.1016/0092-8674(78)90033-8.
The frequency of occurrence of particular repetitive sequence families has been estimated in the DNA of the three sea urchin species Strongylocentrotus purpuratus. Strongylocentrotus franciscanus and Lytechinus pictus using individual cloned S. purpuratus repetitive sequence elements. Cloned repetitive sequence elements as described by Scheller et al. (1977a) were prepared by reassociation of S. purpuratus DNA fragments to repetitive Cot, digestion with single-strand-specific nuclease S1 and ligation of synthetic restriction sites to their ends. The sequences were cloned by insertion at the Eco RI site of plasmid RSF2124, labeled, strand-separated and reassociated with 800--900 nucleotide long unlabeled DNA. Both kinetic (genomic DNA excess) and saturation (cloned DNA excess) estimates of frequencies were made. For nine cloned fragments, the ratio of the repetition frequency in S. purpuratus DNA to that in S. franciscanus DNA ranges from about 20 to about 1. In the four cases examined, only a few copies were detected in the DNA of L. pictus. Estimates have also been made of frequency changes in many repetitive families by measuring the reassociation of labeled repetitive DNA fractions of each species with total DNA from other species. In each reciprocal comparison, the labeled repetitive sequences reassociate more slowly with DNA of other species than with DNA of the species from which they were prepared. Thus it appears that the dominant repetitive sequence families in the DNA of each species are present at lower frequencies in the DNA of closely related species. Measurements of thermal stability have been made of S. purpuratus cloned repetitive sequences reassociated with S. franciscanus DNA or S. purpuratus DNA. Most families have changed both in frequency and sequence, although some have changed little in sequence but show great changes in frequency.
利用单个克隆的紫海胆重复序列元件，已估算出三种海胆——紫海胆、加州紫海胆和花斑海胆DNA中特定重复序列家族的出现频率。如Scheller等人（1977a）所述，通过将紫海胆DNA片段与重复Cot重新缔合、用单链特异性核酸酶S1消化以及在其末端连接合成限制性位点，制备克隆的重复序列元件。通过插入质粒RSF2124的Eco RI位点克隆这些序列，进行标记、链分离，并与800 - 900个核苷酸长的未标记DNA重新缔合。进行了频率的动力学（基因组DNA过量）和饱和度（克隆DNA过量）估算。对于九个克隆片段，紫海胆DNA与加州紫海胆DNA中的重复频率之比在约20至约1之间。在所研究的四个案例中，在花斑海胆的DNA中仅检测到少数拷贝。还通过测量每个物种标记的重复DNA片段与其他物种总DNA的重新缔合，对许多重复家族的频率变化进行了估算。在每次相互比较中，标记的重复序列与其他物种的DNA重新缔合的速度比与它们所制备物种的DNA重新缔合的速度慢。因此，似乎每个物种DNA中的主要重复序列家族在亲缘关系较近物种的DNA中以较低频率存在。已对与加州紫海胆DNA或紫海胆DNA重新缔合的紫海胆克隆重复序列进行了热稳定性测量。大多数家族在频率和序列上都发生了变化，尽管有些家族在序列上变化很小，但在频率上却有很大变化。
