Lamb M M, Laird C D
Chromosoma. 1987;95(4):227-35. doi: 10.1007/BF00294779.
We examined three regions of under-represented euchromatic DNA sequences (histone, Ubx, and 11 A), for their possible correlation with euchromatic constrictions in polytene chromosomes of Drosophila melanogaster. Cloned sequences were hybridized to filters and to chromosomes prepared for light microscopy. Under-represented sequences hybridized to DNA within constrictions and in ectopic fibers. In contrast, adjacent sequences that were fully endoreplicated in the Ubx and 11 A regions in polytene cells hybridized to sites just adjacent to their respective constrictions. For one region (Ubx), sequences under-represented in salivary gland cells were fully endoreplicated in fat body cells. For this particular region, the morphology of the polytene chromosomes differs between these two cell types in that the specific constriction is absent at this region in fat body polytene chromosomes, thus strengthening the correlation between under-representation and chromosome constrictions. Although all three sequences are in regions that have been classified by others as "intercalary heterochromatin," we detect no common functional or sequence organizational feature for these examples of under-represented DNA. We suggest that the lower efficiencies of the replication origins, or special regions of termination at these sites, are the primary cause of the under-replication, and that this under-replication is sufficient to confer the properties of intercalary heterochromatin.
我们研究了常染色质DNA序列中三个代表性不足的区域（组蛋白、Ubx和11A），以探究它们与黑腹果蝇多线染色体中常染色质缢缩的可能相关性。将克隆的序列与滤膜以及用于光学显微镜观察的染色体进行杂交。代表性不足的序列与缢缩区域内以及异位纤维中的DNA杂交。相比之下，在多线细胞的Ubx和11A区域中完全进行了核内复制的相邻序列，与各自缢缩区域相邻的位点杂交。对于一个区域（Ubx），在唾液腺细胞中代表性不足的序列在脂肪体细胞中完全进行了核内复制。对于这个特定区域，这两种细胞类型的多线染色体形态有所不同，即脂肪体多线染色体的该区域不存在特定缢缩，从而加强了代表性不足与染色体缢缩之间的相关性。尽管所有这三个序列都位于其他人归类为“居间异染色质”的区域，但我们并未检测到这些代表性不足的DNA实例具有共同的功能或序列组织特征。我们认为，复制起点效率较低或这些位点的特殊终止区域是复制不足的主要原因，并且这种复制不足足以赋予居间异染色质的特性。
