Angerer R C, Davidson E H, Britten R J
Cell. 1975 Sep;6(1):29-39. doi: 10.1016/0092-8674(75)90070-7.
The sequence organization of the DNA of the mollusc Aplysia californica has been examined by a combination of techniques. Close-spaced interspersion of repetitive and single copy sequences occurs throughout the majority of the genome. Detailed examination of the DNA of this protostome reveals great similarities to the pattern observed in the two deuterostome organisms previously examined in detail in this laboratory, Xenopus laevis and Strongylocentrotus purpuratus. Labeled and unlabeled Aplysia DNA were prepared from developing embryos and sheared to a fragment length of 400 nucleotides. The kinetics of reassociation were studied by means of hydroxyapatite chromatography, single-strand-specific S1 nuclease, and optical methods of assay. Aplysia DNA of this fragment length contains at least five resolvable kinetic fractions. One classification of these fractions, listed with their reassociation rate constants (l M-1 sec-1) is: single copy (0.00057), slow (0.047), fast (2.58), very fast (4000), and foldback (greater than 10(5)). Sequence arrangement was deduced from: the kinetics of reassociation of DNA fragments of length 400 or 2000 nucleotides; the hyperchromicity of reassociated fragments containing duplex regions; the size of duplex regions resistant to S1 nuclease; and the reassociation of labeled fragments of various lengths with short driver fragments. More than 80% of the single copy DNA sequences are interspersed with repetitive sequences. The maximum spacing of the repeats is about 2000 nucleotides, and the average less than 1000. The very fast fraction does not show interspersion with single copy sequences or with other kinetic fractions. The foldback fraction sequences are fairly widely interspersed. The slow fraction sequences are interspersed with the fast fraction, and possibly also with the single copy DNA. The fast fraction is the dominant interspersed repetitive fraction. Its sequences are adjacent to the great majority of the single copy sequences and have an average length of about 300 nucleotides.
通过多种技术相结合的方法，对加州海兔这种软体动物的DNA序列组织进行了研究。在基因组的大部分区域，重复序列和单拷贝序列紧密相间分布。对这种原口动物DNA的详细检查发现，它与本实验室之前详细研究过的两种后口动物——非洲爪蟾和紫球海胆中观察到的模式有很大相似性。从发育中的胚胎中制备了标记和未标记的海兔DNA，并将其剪切成400个核苷酸的片段长度。通过羟基磷灰石色谱法、单链特异性S1核酸酶和光学检测方法研究了复性动力学。这种片段长度的海兔DNA至少包含五个可分辨的动力学组分。这些组分的一种分类及其复性速率常数（l M-1秒-1）如下：单拷贝（0.00057）、慢（0.047）、快（2.58）、非常快（4000）和回折（大于10(5)）。序列排列是根据以下方面推导出来的：长度为400或2000个核苷酸的DNA片段的复性动力学；含有双链区域的复性片段的增色效应；对S1核酸酶有抗性的双链区域的大小；以及不同长度的标记片段与短驱动片段的复性情况。超过80%的单拷贝DNA序列与重复序列相间分布。重复序列的最大间距约为2000个核苷酸，平均间距小于1000个核苷酸。非常快的组分没有显示出与单拷贝序列或其他动力学组分相间分布。回折组分序列分布相当广泛。慢组分序列与快组分相间分布，也可能与单拷贝DNA相间分布。快组分是主要的相间重复组分。其序列与绝大多数单拷贝序列相邻，平均长度约为300个核苷酸。
