Glover D M, White R L, Finnegan D J, Hogness D S
Cell. 1975 Jun;5(2):149-57. doi: 10.1016/0092-8674(75)90023-9.
pDm plasmids were constructed from D. melanogaster and pSC101 DNAs by a modification of the EcoR1-ligase method which insured that each hybrid molecule contained a single segment of D. melanogaster chromosomal DNA (Dm segment). The sequences in the Dm segments of six cloned pDm DNAs were mapped within the D. melanogaster polytene chromosomes by in situ hybridization, and their repetition frequencies within the Dm segment and within the genome were determined. Four of these segments consist of sequences that are confined to single chromomeric regions in the polytene chromosomes and exhibit little or no repetition. The characteristics of this group, and also two of three Dm segments analyzed earlier (Wensink et al., 1974), are inconsistent with tandem repetition models of the chromomere. By contrast, the other two Dm segments contain moderately repetitive sequences that are located in the heterochromatin. One of these appears to be a segment of the Y chromosome in which about half the sequences are nonrepetitive and half are repeated about 33 times per genome, though they are not repeated within the segment. The second contains the DNA coding for 18 and 28S rRNA.
通过对EcoR1 - 连接酶方法进行改进，从黑腹果蝇（D. melanogaster）和pSC101 DNA构建了pDm质粒，该方法确保每个杂交分子包含一段单一的黑腹果蝇染色体DNA（Dm片段）。通过原位杂交将六个克隆的pDm DNA的Dm片段中的序列定位在黑腹果蝇多线染色体中，并确定它们在Dm片段内和基因组内的重复频率。其中四个片段由局限于多线染色体中单个染色粒区域的序列组成，几乎没有重复或完全没有重复。这一组的特征，以及之前分析的三个Dm片段中的两个（Wensink等人，1974），与染色粒的串联重复模型不一致。相比之下，另外两个Dm片段包含位于异染色质中的中度重复序列。其中一个似乎是Y染色体的一个片段，其中约一半的序列是非重复的，另一半在每个基因组中重复约33次，尽管它们在该片段内不重复。第二个包含编码18S和28S rRNA的DNA。
